I need help from knowledgeable car people about a gift for my boyfriend.

My boyfriend is really into cars. He founded a pretty big New Jersey club, all his friends have pretty souped up cars… his is in the shop right now having some fancy new engine and turbo and whoknowswhatelse installed.

I’m thinking I might like to pick something up for his car, for Christmas, but I’m car-STUPID. It’s a 97 or 98 Mustang. Any suggestions?