What do you do when there is no way you can do everything you've promised people you'd do?

I'm feeling real nervous because I've promised people all kinds of things and I'm real worried it won't all work out. I tend to say yes to everything. I'm a laid back 25 year old guy that doesn't do well with commitments and with schedules. I'm at the point of just saying eff it and getting drunk tonight or smoking some weed.