Healthy and unexpensive food
The best way to eat healthy as possible is to prepare your own stuff out of a cooler. Of course you have to go to the grocery more often but it's definitly worth it since the United States (with a few exceptions) seem more like a factory of fast food joints to me (a big juicy cheeseburger is great sometimes though:o).
On my latest roadtrip to the States, I brought a butane camping stove and a cooler that you can plug in the cigarette lighter, it was just great! I think butane is better than propane because it costs less (the stove is about 20-30$, the butane cans are 1$ each in dollar stores, and you don't even need matches with them), it's more compact and not heavy at all. A great mid-size cooler costs about 75-100$ depending on the size you want to have and it is very practical in many occasions (weekend trips, Sunday pic nics with family) plus you don't have to buy ice all the time and find out later that your sandwich has taken a bath while you were driving.
I usually try to pick quiet spots in motels, I bring a table from the room near the window or opened door to cook my stuff. I have a small camping fan that works with batteries, I place it in a certain way so it blows the nocive propane emanations outside and I just cook my stuff right there : pastas, rice, soup, panninis, chicken, vegetables, coffee, eggs, chili, wheat pancakes...
Needless to say, some people often look at me like I'm crazy:-), but most of the time they're friendly and sometimes making jokes on what I'm cooking or about opening a restaurant or something:-) I met some nice folks during my cooking hours:-) : a trucker from Tennessee, a couple from Amsterdam:-)) I always managed to be discreet though, I didn't want to be noticed by the manager and get a warning. I didn't have any problems doing that and I've done it many times, but be careful about the butane, it may be dangerous if it gets into the room. Always leave the window/door opened at least half an hour after you finished cooking.
When I was on the road, I usually stopped at rest areas or nice parks, cooked my stuff and had lunch on a pic nic table, but it is much more simple to prepare a sandwich when you know you'll spend the day driving, because cooking takes a lot of time plus you have to do the dishes (unless you like having bugs and strange odours in your car). If you're the sandwich kind, knock yourself out, but to my opinion, it is much more rewarding to have a full hot meal after a long day of driving.
If you're a fruit/veggie lover, buy one of those small bags of washed and cut carrots, salad in a bag, apples (last very long if they're not bruised), grapes, cherry tomatoes, oranges, cauliflower, peppers, brocoli. Don't bring bananas, they get bruised easily, raspberries (dangerously appealing for a white shirt and likely to fill your cooler with bright red juice), in one word don't bring anything that is easy to spill and not easy to eat with one hand. Put anything that can be bruised inside napkins and stuff it in ziplocs bags.
Be careful with milk, yogurt, eggs, sour cream, meat and mayonnaise, you might get sick in no time if you don't keep them at the right temperature. As soon as it looks/smells strange, dump it in the trash before your whole car smells like that (and it doesn't take long trust me!:-)! You can get small packets of ketchup, relish, mayonnaise, peanut butter, jam, coffee creamier, sugar and other stuff like that in Wal-Marts, grocery stores or along the way when they're available in truck stops, convenience stores, fast food joints. Bring olive oil (with a tight lid) instead of butter to cook your stuff.
If you plan on bringing some meat, pick a bottle of fat free salad dressing (the oily kind) to marinate your stuff. Put your piece of meat in a ziploc bag and put some salad dressing in it with lots of seasoning, salt, pepper, spices. Double the bag and seal them both tightly. your meat will last longer if you marinate it, but don't wait too long. For seasoning, you should consider buying one of those camping containers they sell at Wal-Marts or camping supplies stores with all kinds of spices in it.
Bring lots of nuts, raisins, dried fruits to eat on the road instead of chips and other greasy stuff. You can do your own mix : cereals, nuts, fruits, dark chocolate,... Mix yogurt with that, add fresh fruits (and a spoon of maple syrup if it's plain yogurt) and you have a great healthy desert.
Another last thing, if you like good coffee and plan on going in the south west, maybe you should consider buying one of those espresso camping machine. It's definitly not worse than instant coffee and so much better than drinking that tasteless Exxon coffee (oups, sorry for lovers:)...If you enjoy a good glass of red wine for dinner, Wal-mart (to my surprise)sells a pack of 4 not-too-bad-Merlot small individual sized bottles (I don't remember the exact name). If you're not the only drinker on your trip and you're not planning to hit the road in the following hours, try one of those great Californian bottles (the Fetzer Cabernet for instance!), maybe they're cheaper in the US than they are here! Well you know, I'm just a French frog after all, I can't spend a great day without my cappu and my glass of wine!:o)lol Just kidding!
Have a great trip!
Gas station hot dogs! only 99 cents!
cheap eating while on the road
I don't think most motel owners and operators would approve of the cooking method described above. Some motels have grills and there are often parks with grills.
I NEVER purchase breakfast or lunch at restaurants or convenience stores......I carry a cooler with the stuff I like to eat, and a picnic basket with paper plates, plastic disposable silverware, etc. Its easy to stop and fix a sandwich, or grab a granola bar, fruit and a cold drink almost anywhere along the road.
if you read my post carefully, I did mention that that particular method was risky and unfortunately, not all motels have BBQ's and grills:o). I use that method when I'm off the road and when I'm fed off with cold food. Otherwise, I do the same as you, I eat sandwiches and sometimes cook a meal or two on a pic-nic table in a rest area. However, when I arrive to my motel room only at 8 or 9 p.m., I don't usually feel like going out to look for a public park to cook my stuff, especially when it's dark outside!:o)