People have told me that they are reluctant to give money to these people, because they are concerned that it won't be used for food. My main concern about giving money is that they might have to buy food at a fast food restaurant or convenience store, where they won't get much for their money.
Here's what I do instead: I keep a bag of nonperishable food in my car, just in case I run into someone who is homeless.
I include a can opener, canned food, packaged food (like granola bars), napkins, etc. Nice to add are antibacterial wipes, toothbrush and toothpaste, "Space Blanket" (to keep warm, available at Walmart), a list of soup kitchens and anything else you would want if you were living on the streets.
I try to make the food more or less a balanced diet; including vegetables, fruit, a starch and a source of protein (beans or tuna). A small piece of candy is nice to include. I save samples of cereal or other packaged food to put in the bag.
I gave one of these packets away in Wisconsin during a visit there. The man who received it saw my license plate and said, "Thank you, Utah!" Other responses have been amazed expressions, looks of wonder and effusive thanks.
I've never had a homeless person seem disappointed to get one of these, and if your car breaks down in a deserted area, at least you won't starve. If you like this idea, please share it with others. That's what I'm doing.