Lot of good suggestions here. Don't forget the freezer section of the grocery store: Budget Gourmet, Michelina's and if you're dieting, Lean Cuisine make frozen entrees for one person that are microwaveable and taste pretty good. Take along some fresh fruit and snacks and you'll never miss having to cook.
The boxes are slim enough you can get them in the freezer of a small fridge. If you want to have more than a few days' worth, get a portable freezer you can plug into the lighter or into your rig's wall socket. They come in different sizes and prices so you can get the one that fits your needs. Just a do a search on "portable freezer".