I do not, but if I have a spare bit of money on me I ask them if they would like a hot drink or a sandwich and will buy it for them. As giving cash, IMO, is likely to just go towards funding a bottle of cider or a score of drugs...I know not all homeless are addicts but quite a lot are.
Just reading a thread on DS about this and apparently some reckon giving them food/drink is patronising...I never thought of it like that before and I reckon if I was in that situation I would much prefer someone to offer me food/drink rather than just walk past...but apparently this is dehumanising them and making out you are better than them rather than trying to help