On principle, if I give them anything at all, I give them food, typically fast food. (Because who would trust a sketchy ham sandwich from a stranger?) But I live in the country, so I don't see many unless I go on trips.

When you give bums money, they probably won't use it for anything but booze or drugs (probably crack).

As a side note, I do give generously to talented street performers. There were some really good ones at Pike Place Market when I visited Seattle.