Least? Nothing (so many homeless around here and I know exactly what that money is being used for) but I buy beer for some of them sometimes, especially some that I used to roll with when I was homeless. However, I couldn't ever bring myself to ask someone for food or money. There are plenty of ways to get food for the homeless if they are in any city of decent size.
One night I was walking around downtown and ran into this black dude (I was still semi-homeless, living in a garage with another guy) but I was making great money from a job I had just attained, so after a lil chit chat, he asked for some scrill and I didn't have anything smaller than a 10 on me so I gave him that. He took it whilst looking at it in disbelief, then ran down the street screaming "YES!! YESSSS!!!" over and over. I was so stoned that I lmfao'd and then went on home.