Yes, I'd recommend that you "buy a head" prior to the trip and bring it with you. They take up a lot of room in the box. If you already have the head, you can fit a lot more things that are exclusively Disney items in the box - maximize your purchase!
BTW, I did that several years ago when they used to have a kiosk for My Little Pony. Tons of exclusive Disney stuff for MLP - lots of princessy stuff for the ponies. My niece thought I was a rock star! I bought at least two of each princess "outfit" piece so that she could play with her friends. So fun. You should have seen us adults sitting on the floor, all trying different ways to stuff as much in the boxes as we could.