Knife: Just a small pocket knife will do, for cutting rope, clothing, bandages, etc. And there are still those cave zombies to worry about...
Knife: Generally blades under four inches are allowed on board, but check before you go. The smart play would be to get a Swiss Army Knife for all the extra gadgets.
A knife sale for back to school? I should not eat a fail this sweet. It might give me high fail-esterol.