This will get buried in the jokes, but here's my serious response:

Context: I work in AM in Europe (DACH), taking L1 in February after being given guidance, incentive, and support from my firm to do so.

Our company has close ties with the local CFA community, and what will frequently happen is that they organize a free lunch and drinks throughout certain exam days right across the test center. It's a chance for candidates to blow off some steam after test-taking, and to network. I went this year to talk with other candidates about their experience taking the CFA. It's a great opportunity to see how the CFA has shaped people's careers. Many charter holders attend these events, mostly to reminisce and offer unsolicited advice. With that said, the standard attire has always been slacks or jeans, with a button-up.