Here's my $.02:
Go for a walk.
Go to the movies.
Go on a hike (depending on where you are).
Go people watch.
Sneak into a local hotel pool and go swim. Or skinny dip. Whatever.
I guess it really depends on where exactly you are. And a lot of things that are options will still have other people drinking. It's just a matter of keeping yourself separate from that element.
Best of luck! I hope you end up having a lovely evening.
B'sT