Do whatever you feel like doing!
It's your day and if you don't wanna do some big thing, then don't! Go shopping, pick up stuff to make (or have someone make for you) a favorite dish or hit your favorite place out, grab a book and read outside, fill the tub with water and bubbles and fill the bathroom with candles and hang a do not disturb sign... whatever floats your boat, dear! Do something that makes you feel good - just make sure (in a nice way) that others around you kinda know that it's your day so maybe you'll be in charge of the remote and won't be stuck doing the dishes, that kind of thing
On my actual bday this year, I went to an ice hockey game (the Flyers AHL team, the Phantoms) and wore my jeweled tiara (yes I'm 24 haha) to the game and then my dad and I got famous Philly chessesteaks from Genos - it was exactly what I wanted to do! My bday "gift" from my parents is actually good tickets to next week's Kenny Chesney concert in Philly - so I'll be celebrating again next Saturday with my mom, thousands of fans and my favorite artist