My disclaimer is that we didn't visit the museum but hear me out folks - the gift shop is AWESOME. We popped in for a quick look and we're delighted to find "bubbler" (because a fountain is what you throw coins in, dont'cha know) and "Brandy old fashioned" t shirts. They even have a Fish Fry Friday one.
There are books of course, and a nice kids area with educational things. Myself? I couldn't pass up a pair of socks covered in badgers holding lilacs.