If you're a bridesmaid or a groomsman in a wedding, the only thing I'll tell you is please, please, please understand that you're allowed to say no. We often think that if we take on that role, we have to say yes to everything, but if there's something you can't afford, you don't want to do, or you don't have time for, make sure you say no.
How do you say no? You simply say, hey, thanks so much for asking me to do that, but at this time, that's just not something that I can swing. Happy to help in other ways. Keep it easy, keep it friendly, but make sure you stand up for yourself and say no.