Graduating Husband Gift

So my husband is graduating with his Masters in Physics. This Friday he has his thesis defense and I want to get him something to show him how overwhelmingly proud I am of him. He has worked so hard to achieve this goal.

I’m just looking for some gift recommendations. He really isn’t a materialistic guy- basically a hippie that rocks at math and science, so gift giving has always been hard when it comes to him and I’m coming up with no ideas.

Any graduation gift ideas for men are welcomfe!