Take Two, They're Small
For the Show Day originally, I think, referred to racing at the track.
To celebrate the day, you could go to the track, if there's one nearby. If there are no races being run, well, that's just the way it is.
You could instead take in a movie at the theater or a play at the other theatre.
In any case, it's best to take someone with you, as in two for the show.
If you're into events like dog shows, I guess they could count towards celebrating today too. I think you would have to actually attend one though, not just watch one on TV.
I also think that renting a video doesn't count like going to the theater does, even though that's probably a lot cheaper.
Things like showing off or showing anything else are not in the spirit of the day. This is not to say you can't do them, but they just don't count.
Get ready for tomorrow.