You can "measure" which hide size you need with any number of containers at home. Cereal bowls, plastic tubs, a hat... anything. Then take that item with you to the store instead of your python. There's no need to carry him to a store that could have sick snakes or mites or anything, without proper heat and such.

If you don't have a tupperware to use for needed trips, go get one. It would cost you a dollar. Then you'd have a secure thing to carry him in. Poking holes in plastic is easy.