Where I live, I don't see many homeless people. If I do, it is because I am in a part of town where it's probably not safe to be alone, iykwim. Only one time, when I was approached, I was studying in the university and we were right by the food court area in the middle of winter. Guy really wanted a baked potato. I bought him one and actually sat and talked with him for a while. Very interesting.
Another time, in the Uni, I was approached by someone who said he ran out of gas, and could he please have some money...I wasn't really sure what to do. I gave him a $20 (it's all I had), and he promised to meet me the next day to pay me back. Never showed, of course. I felt sort of gullible, but at the same time, I don't really regret it.
I'd always rather err on the side of being overly generous/compassionate (at the risk of being "wrong"), than not.
I'm not so great about keeping food in the car, and since I don't see people in need that often, I actually keep a $5 McD's card in my glovebox. Not that healthy, I know, but at least I know they are fairly readily available and the person can get something to eat.