The issue is convenience. I have the same situation -- no food budget, I'm downtown with all the restaurants, and on the way home there's nothing but junk food drive-throughs. Why should I shop and cook when there is so much right available to me with zero effort? So the solution for me has been to food shop and then cook all day one weekend day and portion everything out, so in the morning I know what I'm going to eat, I can grab something I made myself from of the refrigerator and bring it for lunch, along with some fruit for snacks (which would be, for example, grapes already picked off of the bunch and washed, or an orange already peeled and wrapped with a damp paper towel) -- just spend one day making it so I don't have to think about what I'm eating the rest of the week. That's what works for me.
It's just that I so hate the kitchen...but what must be done must be done.