I found this online today at a blog called Mr. Chalk. This is a blog from "over the pond," as the guy talks about pounds instead of dollars and a lot of the spelling is different, but pretty funny.
I'm thinking now that I really shouldn't just cut and paste the guy's blog entry, and that might be seen as a blatant act of plagiarism, even if I am citing my source. So instead, I'll just point you in the right direction.
Mr. Chalk has written a field trip permission slip that expresses everything that a teacher has ever wanted to include in such a form. Nothing is held back here. A few of the comments and references are cringe worthy (such as the comment about the music teacher), but overall this is pretty darn funny.