If you must eat out at a resauruant or fast food, its perfectly okay.
If you choose a fatty fast food place, to name a few, burger king, mcdonalds, or wendys, make sure to get a grilled chickan salad with no dressing. Dressing will waste your workout, puting the fat right back where its been burned. I find the mandarin orange salads to be quite tasty with out any dressing at all. Stay away from low fat dressings as well, it goes straight to your thighs and belly.
Another great place would be Toojays. Its a deli, that provides a healthy part of the menu, with salads, wraps, and platters containing low low fat ingrediants. Also a good fast food place is Chickan Kitchen, that is all grilled chickan. Be strong and refuse pizzas, or fatty crispy fried chickan, and stay on the healthier side. Even pizza places have grilled chickan sandwiches, which you can ask for it w/o mayo. If no low fat is available at the restaurunt, go for the veggietarian items. Veggies have no fat!

Man cannot live without pizza. Such a proposition is unreasonable.

You can eat pizza, just don't eat the whole thing. The next day eat tuna sandwich on whole wheat and a salad.

I agree you're not likely to eat too many calories if you go veggie. Animal fats are always the biggest problem for accumulating more calories than you think.