I have always donated my winnings back. When I attend a benefit, it is because there is a need. My friends and I all buy tickets and I can count on one hand the number of things we have kept. Haircut, no thanks, I have my own hairdresser. Wine, I don't drink wine. 50/50? One time it was 75 bucks and once it was 200 range, we have always just donated it back.
With that said, we always know who or what the benefit is for. We don't "blindly" attend. We have a great time eating and drinking and seeing friends. We aren't there to win money or anything. We are happy leaving with empty pockets.
Sorry, I left out my reason for posting. There should not be pressure to give it back and to pressure someone is rude. And there is nothing wrong with keeping it.