I'm a big fan of subtle bitcoin merch. Lightning.store has a lot of really good low key stuff that you wouldn't necessarily know is bitcoin unless you know. fomo21.com is good too.

For example I have a plebchain radio shirt as well as a shirt that says "Satoshi Boat Tours. It's been 1 day since our last accident" (slightly less subtle but still good). Supply formula shirt is another good IYKYN shirt.