Many supermarkets in urban areas in the U.S. have a salad bar. You can fix yourself a nice salad and then go to the deli to buy sliced meat to put on top of it. There is also usually hard boiled egg available on the salad bar. They also usually have some already washed strawberries and pieces of melon. Just remember that they charge for the salad bar by the ounce and some ingredients weigh a lot more than others! Usually there is a scale nearby so you can weigh it yourself and get an idea of what it will cost before you get to check-out.

As someone else already wrote, many supermarkets also have already cooked rotisserie chickens.

I have found Boston Market to be a good, inexpensive fast food place while traveling in the U.S. You can get half a small chicken with two different vegetables as sides for $6 or $7 -- either to eat there or to take out. Their sliced turkey is also good. If you go to Boston Market, tell them not to give you the cornbread! It's great, and very hard to resist if you take a bite.

Enjoy your trip -- you are going to some great places!