If they tell me they want to buy drugs, cigarettes, or booze, I'll give them a dollar sometimes, but usually I realize that this money can buy me tobacco or booze, so no. If they want food, I certainly won't give it to them. They can usually get that for free from homeless shelters or soup kitchens or whatever. Also, if they are extremely repulsive looking or smell funny, I probably won't give them anything because they'll try to shake my hand and I'll be totally grossed out. :P