If your job involves any activity at all (walking, etc), double shifts will mean double the amount of activity. It counts, even if it doesn't take place in the gym. I'm not saying you shouldn't try to get some other exercise, too, just that you shouldn't beat yourself up about not getting it during this period of double shifts.
If your job is sedentary, well, that's more of a problem. Try getting out at breaks, particularly the ones early in the day when you still have energy. Your 30 minute walk needn't take place all at the same time.
Regardless, you can do something about eating. Instead of fast food, why not stop by the grocery store? Modern grocery stores have a wealth of food choices for people on the go: fruit, vegetables, single-servings of cottage cheese and yogurt, deli meats, often a fish bar with precooked shrimp, krab with a K, sandwich stations (hold the mayo!), salad bars, roasted chicken, hot-food deli counters that might have at least one healthy option (a lot of it isn't)... the list goes on. You can get a lot more nutritional bang for your buck in about the same amount of time as it takes to stop by McWendys King.
If a grocery store isn't as close as fast food, well, even the dive-iest of convenience stores will carry milk, cottage cheese, and usually some apples and oranges. There are always choices.