I did a solo East to West (Virginia to Astoria, Oregon) about 6 years ago. It was totally awesome. The Adventure Cycling maps are really great - I did a mix & match of routes, so got the relevant sections. There is a need to have a plan but also be flexible - as Karla says, sometimes there really is 50-90 miles between places to get food/water and even then it's just a gas station (with a casino in the back
). Also, it's useful to know that certain things are very different in the US compared to the UK. If I see a 'Road Closed' sign in the UK, I know that 99.9% of the time I will be able to get off the bike and push. In the US, they might have completely removed the road for 10 miles.
I stopped in a lot of gas stations for food. Once out of towns, that resulted in a surprising number of people talking to me. I also found that I had surprisingly few negative interactions with motorists. Although they aren't expecting to see you, sometimes that results in them just taking a massively wide berth.
When planning your route, make time to actually see stuff. There are a lot of really stunning natural features that aren't well known and so can be quiet spots. I also quite like some of the random industrial heritage in some of the towns in the mid West - they haven't grown so much that buildings from the foundation of the town have been removed.