I needed a fast response, since it was 10:30 at night when I posted this. So I asked on a more populous forum.

I did take it to school, and released it the next day. On the advice of a person on the other forum, I kept it in a Tupperware container. I gave it a little bit of water, after taping a glue stick to the bottom (which left it tilted to the side so the water pooled to one side.

My old biology teacher actually had a funky little plastic terrarium (with a little surfboard!) and offered to take him, but later told me she wouldn't really know how best to take care of it. I released it just now. It was one of the hardest things I've ever done.

EDIT: He might have been pretty dried out when I first picked him up, because when I gave him some water he appeared to get a bit greener. This was after I took the picture. Also he was not in IMMINENT cat danger. The cats had not yet found him, but I'm sure they would at some point.