The Saga Continues. (It'll Never End.)
A Galaxy Far, Far Away Day is an obvious reference to Star Wars. To celebrate, you just as obviously don't have to literally travel there. Figuratively is fine.
If you haven't watched the original SW trilogy in a while, today would be a good day to do so. That would count as a celebration.
Actually, anything you do today that is even remote related to SW counts as celebration.
Quoting lines from any of the movies is acceptable.
Dressing up as any of the characters (except Jar Jar) is acceptable.
Playing with SW toys (especially Lego) is acceptable.
Reading the original books is acceptable. Reading related fanfic is marginally acceptable as a last resort.
Merry Christmas.