We eat a lot of frozen and refrigerated burritos and wraps. I'm really lucky, because there's a lot of good local options at the co-ops here in Portland, but the Cedarlane brand Beans Rice and Cheese burritos are nationwide and available at Costco last time I checked. They're 290 calories, very filling, pretty tasty... and it only takes a paper towel and about 2 minutes in the microwave to make them. I also buy strawberries and cherry tomatoes by the pint and tear through them whenever I feel like I just need to EAT. Whole strawberries are about 140 calories for an entire pound, and cherry tomatoes are around 100 for a pint, I think. I tend to swing by grocery stores when I'm on the go and hungry, it doesn't take much more time than fast food, and it gives me a huge selection of fresh produce and salads to choose from. The Safeway deli's even stocking little individually wrapped hard boiled eggs now, and that's the ultimate meal-on-the-go!
Edit: I just realized that the "fresh strawberries on the go" thing only works for me because I usually don't wash my produce before eating it... usually buy organic, though, and I'm a firm believer in building up my immune system. I'm kind of an anti-germaphobe, I guess. Sorry if that grosses anyone out.