You might print out/makes "slides" of photos of Tshirt quilts (made by others) that are similar to what you intend to make. The auctioneer can project those on a screen. Say that you'll need at least 16 shirts but no more than )fill in the blank based on how large you're willing to go).

If you're able to do a table display, I recommend spreading 1-5 T-shirts from your high school on the table. Then place some photos of similar quilts in very cheap stand-up plastic frames. If there won't be a table display, look into doing something similar with a video "slide."

Almost all people are visual. If you give them enough visual information, well-presented, you'll get more bids.

Good luck!