Welcome to the forum! Retired AF wife (and former AF brat) here. 
I’m thinking squadron patches and such would be super popular. I did a security police badge for my dad a while back, and he lamented that he wished he’d had it to put on his desk before he retired (high praise, from him!). I also created a vector version of my husband’s old branch logo, and have given a lot of creations to his old AF buddies with it engraved on them.
It was kind of a lot of work tracing it into vectors, but once you have that done, you’re home free to start churning out layered copies, engraved keychains, picture frames, and whatever else comes to mind!