If I'm working or others have plans, I find a way to enjoy the evening or the day whatever way I want. Doesn't have to be all that extravagent.
Whenever someone has free time, I make some basic plans with them, which mostly consists of drinking and watching movies.
Basically celebrate it whatever the hell way you want and is most convienient to you on the day. Afterall, it's the one day of the year where everything is about you.