I would use them to pay for someone else's meal, but be prepared for some funny looks.
Before I went this past May I had read a thread on here about 'nice things you could do for strangers at WDW'. I was so impressed and decided I wanted to do some of the things suggested. At Aloha Isle I heard the people behind me trying to decide between the dole whip float and the plain dole whip, saying the float was more expensive so they'd better get the cone. When I ordered my float I bought three more for the people behind me. As I was walking off the little boy said "Why did she do that' and the dad said he didn't know. I just smiled and said because my GD couldn't come with me, but I knew she would want a dole whip float, so decided to buy one for the first kid I saw, along with his family. They were smiling, but looking at me funny as I winked and walked off. At POP Century one morning there was a young couple with bride and groom ears on behind me. I paid for their breakfast and got another strange look. Also at the MK I bought a balloon and started looking around for a kid to give it to. I saw one who looked exhausted and was crying. I asked the parents if they would do me a favor telling them I had bought the balloon, but then realized they weren't allowed at the AKL because of the animals and asked if I could give the balloon to their daughter. The tears immediately stopped, but unfortunately I got caught. As I was in the bus line for POP they were just a few people ahead of me. The little girl saw me and said 'hey lady you're in the wrong line, this line is for POP not AKL'. I laughed and said 'you're right' and got out of line until the bus came and left. The parents again smiled, but gave me a funny look. I'm saying all of this to say that some people are suspicious when others do something nice for them, so if you're giving away free meal credits be prepared for the suspicious looks. Too bad some people can't expect the good things that happen for them and always expect the bad. Spreading a little magic makes the giver feel better than the receiver sometimes. I was traveling solo that trip and really enjoyed surprising people with just a little pixie dust.