[Looking around, Marty's not really coming up with anything to seal the hole, either. He goes through his mental rolodex of spells, but nothing is really all that useful against... tentacles, not unless he wants to set the box on fire, but then that would open up a whole other can of worms-- namely: what would they do with a burning box in the middle of a bookstore. He's no expert on fire, but he's pretty sure that bookstores are extra flammable.]

How? Stack books in front of it? Tip the box over?