Yep. I have cans of almonds and jerky at home, in my desk at work, and in the glovebox of my car. My girlfriend INSISTED on going to Davanni's this past weekend (pizza/pasta place in Minnesota) and that would normally spell great trouble, but I got a half hoagie, no cheese, and double the chicken breast. Wasn't terribly bad, and if that's the worst thing I eat in a day then that's alright. If you absolutely HAVE to eat fast food, then get some white meat (not fried or breaded) and no mayo, cheese, etc. I don't even usually eat the bun if I get a chicken sandwich.
But like JKurz1 said, your best bet is to plan ahead and bring resealable bags of food wherever you go.