I read a book where a homeless man shared a scam called a "food drop."
The scam works like this. Scare up enough money to buy a hamburger, which is usually pretty easy. Then go to some building and hang out in front of the building right before lunch. Take a bite out of the hamburger, then put it in a trash can.
When people start coming out for lunch, start going through the trash can. "Find" the hamburger and start eating it. People will shove money at you so you don't have to eat garbage.
So you even have to be careful giving someone a sandwich. Like another poster said, make sure they eat it in front of you.
Our church associate pastor has a daughter living in college in Austin. She is stopped regularly by the street people. She carries a pair or two of new socks and oranges which she hands out the window at stop lights, etc..
Sensible idea. Scurvy happens to those with poor diets.