Figuring out what to carry on a cross-country trip may seem daunting, but it is probably the easiest thing to figure out and adjust as you go along. Every cross-country cyclist faces the tradeoff of carrying more gear and being better prepared for different situations or carrying less gear and traveling lighter and faster. Your personal budget and tolerance for roughing it will dictate that tradeoff.
Camping versus motels:
Unlike most cross-country cyclists, I did not carry any camping gear on my trip. In retrospect, carrying some rudimentary camping gear might not have been a bad idea; it allows you more flexibility to adjust your mileage. I made motel reservations in advance - usually by several weeks - and therefore had a schedule to keep. The distances between lodgings in the West will often dictate riding longer or shorter distances than you might otherwise want to. Moteling is significantly more expensive than camping, but does offer some comforts at the end of the day: a bed, air conditioned room, shower, and TV/wifi. However, given that you can always opt for a motel, the only reason not to carry camping gear is to reduce weight.
Equipment:
A good road bike is a prerequisite for any cross-country trip. Your bike will cover a lot of miles and take a beating; do not attempt a cross-country trip on $50 bike from Walmart. A decent bike shop will carry touring bikes designed for long-distance riding. These bikes are engineered to attach both front and rear panniers, use cantilever brakes which are stronger than caliper brakes on a road bike, and sport the gearing for climbing comfortably while carrying 40-50 pounds of gear.
However, instead of buying a touring bike, I purchased a road bike: Specialized Secteur Elite. With a carbon fork and stem, this bike is somewhat lighter than a touring bike but has attachment points for a rear rack. Road bikes are perfectly fine for a cross-country ride so long as you do not overweight the bike; the wheels are not designed for heavy duty touring. I carried all my gear in two waterproof Ortlieb rear panniers attached to a Topeak rear rack and rear trunk bag on top.
One thing to be aware of if using a road bike is that the gearing may not be right for getting up the various climbs you encounter. My rear cassette was originally a SRAM 12-26 and even in the lowest gear, I had a lot of trouble getting up the steep grades in Pennsylvania. In Bozeman, MT, I switched the cassette to a Shimano 12-30; the larger cog (30) in the back made it considerably easier to climb. Do something I did not do: ride your bike fully loaded several times before departing.
Technology and electronics:
A good smartphone will greatly enhance a cross-country journey. A smartphone is particularly useful for finding the distance to the next food/gas station options on the route, or finding an alternative route in suburban/urban settings. In some areas of the West, cell service becomes either spotty or unavailable. I went to the trouble (and expense) of renting a satellite phone, but, in retrospect, I would only carry a satellite phone if you are cycling in remote, untraveled areas like gravel trails out West or touring in remote areas like Alaska.
Another useful gadget is a GPS for mapping and navigation. I bought a Garmin Edge 800 and, before each day's ride, I loaded the course route. With the exception of bike trails, the route maps appeared up to date and easily directed me through residential roads and rural country roads.
Clothing and other gear:
On a cross-country journey, you will need to be prepared to cycle through all kinds of weather. A couple days in Pennsylvania had temperatures in the 40s while several days out West, temperatures peaked near 100 in the afternoon. Cold weather gear may be needed depending on when you leave, a waterproof rain jacket is a must, and sunscreen essential. I carried only sandals as footwear, shorts and a T-shirt to wear when not cycling to minimize weight. I also carried my MacBook Air cross country - a unnecessary but nice indulgence at minimal additional weight.
Getting chased down by a dog is something that most cyclists can attest to. Most of the time, owners would manage to stop their dogs from chasing after me, but I did encounter cross-country cyclists who had been either chased for awhile or had dogs try to bite them. Pepper spray is an option which I carried, but many cyclists just recommend using your water bottle to spray the dog or simply trying to outrun the dog.
Bike repair and maintenance:
Before leaving on my trip, I invested a fair amount of time learning how to address a variety of possible bike breakdowns. However, as it turned out, the only problem I encountered were a couple of flat tires. My friend Andrew got a flat on the open road, riding into Minneapolis, while my bike took a flat on a day off in Miles City, MT. Needless to say, knowing how to fix a flat is a must and very easy to learn and practice. My tires were puncture resistant hard case tires made by Bontrager or Specialized. I replaced my tires every 1200 miles, though this was probably overly conservative. A hand pump, tire levers, a multitool, and extra tubes are an absolute minimum for a cross-country ride.
Beyond flat tires, I also learned how to adjust the derailleurs (for smooth shifting), remove a cassette, replace broken spokes, and true a wheel. I carried extra spokes, a spoke wrench, and a cassette adaptor for replacing a broken spoke, but I did not carry a chain whip and wrench for removing the cassette on the rear wheel. You can continue to ride with a broken spoke though you risk permanently damaging the wheel.
Cross-country rides take their toll on the chain - regularly cleaning and lubricating the chain (especially after cycling in rain) will increase the chain life and reduce drag. However, it is probably prudent to replace the chain once during the trip. A chain tool and replacement pin should be part of your spare parts, especially for longer rides or rougher conditions.
Camping versus motels:
Unlike most cross-country cyclists, I did not carry any camping gear on my trip. In retrospect, carrying some rudimentary camping gear might not have been a bad idea; it allows you more flexibility to adjust your mileage. I made motel reservations in advance - usually by several weeks - and therefore had a schedule to keep. The distances between lodgings in the West will often dictate riding longer or shorter distances than you might otherwise want to. Moteling is significantly more expensive than camping, but does offer some comforts at the end of the day: a bed, air conditioned room, shower, and TV/wifi. However, given that you can always opt for a motel, the only reason not to carry camping gear is to reduce weight.
Equipment:
A good road bike is a prerequisite for any cross-country trip. Your bike will cover a lot of miles and take a beating; do not attempt a cross-country trip on $50 bike from Walmart. A decent bike shop will carry touring bikes designed for long-distance riding. These bikes are engineered to attach both front and rear panniers, use cantilever brakes which are stronger than caliper brakes on a road bike, and sport the gearing for climbing comfortably while carrying 40-50 pounds of gear.
However, instead of buying a touring bike, I purchased a road bike: Specialized Secteur Elite. With a carbon fork and stem, this bike is somewhat lighter than a touring bike but has attachment points for a rear rack. Road bikes are perfectly fine for a cross-country ride so long as you do not overweight the bike; the wheels are not designed for heavy duty touring. I carried all my gear in two waterproof Ortlieb rear panniers attached to a Topeak rear rack and rear trunk bag on top.
One thing to be aware of if using a road bike is that the gearing may not be right for getting up the various climbs you encounter. My rear cassette was originally a SRAM 12-26 and even in the lowest gear, I had a lot of trouble getting up the steep grades in Pennsylvania. In Bozeman, MT, I switched the cassette to a Shimano 12-30; the larger cog (30) in the back made it considerably easier to climb. Do something I did not do: ride your bike fully loaded several times before departing.
Technology and electronics:
A good smartphone will greatly enhance a cross-country journey. A smartphone is particularly useful for finding the distance to the next food/gas station options on the route, or finding an alternative route in suburban/urban settings. In some areas of the West, cell service becomes either spotty or unavailable. I went to the trouble (and expense) of renting a satellite phone, but, in retrospect, I would only carry a satellite phone if you are cycling in remote, untraveled areas like gravel trails out West or touring in remote areas like Alaska.
Another useful gadget is a GPS for mapping and navigation. I bought a Garmin Edge 800 and, before each day's ride, I loaded the course route. With the exception of bike trails, the route maps appeared up to date and easily directed me through residential roads and rural country roads.
Clothing and other gear:
On a cross-country journey, you will need to be prepared to cycle through all kinds of weather. A couple days in Pennsylvania had temperatures in the 40s while several days out West, temperatures peaked near 100 in the afternoon. Cold weather gear may be needed depending on when you leave, a waterproof rain jacket is a must, and sunscreen essential. I carried only sandals as footwear, shorts and a T-shirt to wear when not cycling to minimize weight. I also carried my MacBook Air cross country - a unnecessary but nice indulgence at minimal additional weight.
Getting chased down by a dog is something that most cyclists can attest to. Most of the time, owners would manage to stop their dogs from chasing after me, but I did encounter cross-country cyclists who had been either chased for awhile or had dogs try to bite them. Pepper spray is an option which I carried, but many cyclists just recommend using your water bottle to spray the dog or simply trying to outrun the dog.
Bike repair and maintenance:
Before leaving on my trip, I invested a fair amount of time learning how to address a variety of possible bike breakdowns. However, as it turned out, the only problem I encountered were a couple of flat tires. My friend Andrew got a flat on the open road, riding into Minneapolis, while my bike took a flat on a day off in Miles City, MT. Needless to say, knowing how to fix a flat is a must and very easy to learn and practice. My tires were puncture resistant hard case tires made by Bontrager or Specialized. I replaced my tires every 1200 miles, though this was probably overly conservative. A hand pump, tire levers, a multitool, and extra tubes are an absolute minimum for a cross-country ride.
Beyond flat tires, I also learned how to adjust the derailleurs (for smooth shifting), remove a cassette, replace broken spokes, and true a wheel. I carried extra spokes, a spoke wrench, and a cassette adaptor for replacing a broken spoke, but I did not carry a chain whip and wrench for removing the cassette on the rear wheel. You can continue to ride with a broken spoke though you risk permanently damaging the wheel.
Cross-country rides take their toll on the chain - regularly cleaning and lubricating the chain (especially after cycling in rain) will increase the chain life and reduce drag. However, it is probably prudent to replace the chain once during the trip. A chain tool and replacement pin should be part of your spare parts, especially for longer rides or rougher conditions.