Here is one of the major adulthood lessons I've learned so far -- stop feeling obligated by every social invitation that comes your way. I think a lot of times, people waste significant amounts of their time and money by doing things out of an unfounded sense of obligation. The sad part is the waste of precious time and money, and the ironic part is that no one *really* cares about what you do.
I don't know about you, but I have a VERY long workday. This means that from Monday to Thursday (not counting time allotted for sleep) I almost never have more than a couple free hours at a time. This makes the weekends uber-precious. This also means that all the errands and other general taskers that I need to do during the week inevitably get pushed off to Saturday and Sunday. Now, don't get me wrong -- I love catching up with friends for a pint of beer, a meal, a coffee, or whatever. But at the same time, as I've already stated, my free time is rare, and I treasure it,so I don't necessarily jump on every chance to go out -- especially on the weekdays, but even on the weekends as well.
And here's what I've learned -- no one *really* cares. People may call to see if you're around, but if you're not, or you're busy, or whatever, they'll get along just fine without you. So my advice to readers is this -- shed your unfounded feeling of obligation to say 'yes' to things. Don't feel like dropping half a month's pay to attend some distant cousin's wedding on the opposite coast? Don't go. And guess what? Chances are, no one's going to notice that you're not there.