I have a follow a criteria, because we don't know the circumstances of these people, and as nox says, 'There bit for the grace of God',
I don't give if they have a pet with them and if they are smoking, I have in the past, gone to a shop, and bought them a coffeee an sandwiches.
But the other day, there was a chap just sitting on top of his belongings, nursing a cuppa. he looked so down, that I couldn't stop myself, I gave him some money, and the look of gratitude on his face assured me that this time, i'd done the right thing.