I venture that, if you counted calories, you could eat, like, hamburger patties, with onions and some french fries (no bun), and supplement with a multivitamin, and be mostly ok. Fat/grease isn't completely awful, so long as you actually include it in your count, and stick to under 2,000 kcal/day. You'll just find that relatively small volumes of food are required.
Potatoes you don't want to go overboard on, but as carbs go they're among the better ones -- better than bread -- because their glycemic index is lower. And with the skins on they have nontrivial vitamin/mineral content.
If you did a little more cooking at home, particularly with beans (not in sugary ketchup, just beans with butter and spices -- salt, pepper, cumin, say), then you'd be a bit better, on account of the fiber. Add frozen or, failing that, canned vegetables, and you're almost actually good.
Often you can find canned chilli that's nutritionally pretty good; just make sure it doesn't have sugar; they put sugar in too much stuff.
Getting more of your calories from nuts is also a good option. Surely you can get a jar of peanuts? A large handful is 300 kcal. A couple of those spaced over the day can fuel you quite well with a slow burn.
The car-deprndrnce of the country is an issue; you probably would not naturally walk far enough. If there's some way to schedule in about two miles a day -- walk to the gas station for a black coffee? -- then that'd help to maintain some minimal baseline levels of activity.
Stick to the calorie count and maintain some (frankly modest) level of light exercise and you can maintain your health in a fairly wide range of circumstances.
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I get what you mean though. There's a real class difference. You go to higher class places and there are plenty of salad places around. You go to low class places and there's fast food junk. The latter isn't even much cheaper. It's enough to make you start wondering if people are in the classes they are because of the standards they have. That's not a comfortable thought, but, when you look at how all the bankers seem to also have good gym routines, you really do start to wonder.
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You don't need to do anything superhuman though. You don't need to even summon the willpower to hit the elliptical machine every day. If you just think about what you're eating, count calories, reduce sugar and fast carbs, and walk a bit, you'll do pretty well.