I have to admit I've done that a lot. Being a visible minority has it's advantages every now and then.
If you happen to have any, food is something that many/most homeless won't turn away from. For example, when I was still in university, every now and then myself and a few buddies like to go out for wings. After polishing off 5 or 6 dozen we usually take home the 3 or 4 wings that were leftover, and if we ran into any homeless people asking for change on the way home, we'd just give them the wings.
[HIDE]NB. The above answer was part serious/honest, part youthful douchebaggery on my and my buddies' part. [/HIDE]