I have and will every single time. However, I only give food.
I feed my dogs Merrick and I buy the 20 lb size and I purchase 5 at a time. We have a homeless couple that sit in the burger king parking lot by wallys. I saw them a few months ago when stopped at the light. I drove up to burger king where the woman was sitting with a very skinny dog (was part grey hound I think but still looked boney) I had just been across the street and had picked up my 5 bags of Merrick, bully sticks, and treats for the dogs (6 months worth). Well, I bought whopper meals for the couple, and gave them a bag of the food. Actually I opened it up, put it in the dish while she went and got some more water for the dog. I also offered a free visit to my vet for shots of which they took me up on. So that stop may have cost me in the short run but I know that dog had food for at least 3 weeks and had its shots and a visit to my vet. Later that month I got a call from my vet. They gave the dog a 40 pound bag of science diet and thanked me for caring about a strangers dog.
To me I could care less if they do drugs, the dog loved them and was soo sweet. I did it for the dog and I know I did right.
But I would not give cash. In that way I feel that I did not contribute to them purchasing drugs but gave them a cheap meal and their dog got way better

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Most of us are 1 pay check away from being homeless. So I hope if that ever happened to me, that someone would at least be kind to my dogs..