Just a few of ideas off of the top of my head...
You could do a game night basket and pick up some of the more "modern" board/card games like Quixx, Carcassonne, Quirkle, Blokus, Forbidden Island, Ticket to Ride, or Bohnanza along with some card games like No Thanks!, Monopoly Duel, Sushi Go, Guillotine, Exploding Kittens, etc.
A craft/journaling basket (likely more geared to girls). My high school, now college-aged daughter loves doing Smashbooks. "Adult" colouring books are also currently all the rage. You could add coloured pens and pencils, stickers, etc.
You can also do a colour-themed basket...perhaps in your school's colours where everything in the basket (while potentially unrelated), is in those colours. Think of a main item or two and then shop for snacks or other items in packaging that fits your colour scheme. For example, a basket with a yellow theme might include items like Bananagrams, a notebook with a bright yellow happy face on it, some Butterfinger chocolate bars, etc. (I apologize...these aren't very inspired ideas, simply examples.)
And finally, you can do a fun and games basket with things like a Rubik's cube (or similar puzzler), Thinking Putty, some quality snack items, card games (see above), puzzle books (Pocket Posh has some good ones), and any number of similar type items like what they sell at Marbles: The Brain Store.
Good luck with your raffle!