Yes, I have both buyer's and not buyer's remorse! I drive myself crazy... down to the tiniest every day choices, ack!
As others have mentioned, making a list, really, really helps. If I ever see anything online or in the store I just write it down, that I really wanted it, I don't buy it, unless it was already on the list, ever... even if it's on super, duper super sale, because it doesn't matter, I can regret buying things just as well as not buying them so I don't let the stress of regreting not buying it force me into buying it, I just can't buy anything on a whim, ever. It's worth spending more to have no remorse... I've decided that, I've decided my mental/emotional state is worth paying more for, yes it is! As far as craigslist or thrift stores go, I have a list of things I want and unless I find something that fits that list I don't buy it... again, doesn't matter how great a deal it is, or if it's almost exactly right... I've found in every case I can make do *without* just as easily as I can make do with something that is almost not quite exactly what I need.
Beyond that, you just have to let go. Yep, oops, should've bought that, shouldn't have bought this... oh well! I know, it's so much easier said than done, but it is really easy to say to yourself... 'oh well, moving on! just letting that one go!'... and eventually it does sink in... I think...
Also, I think it's important to focus on the positive of what's already done... sure, you have more time to shop for a 'better' dresser, but now you don't have to, no more worrying about that and having to be on the lookout!... sure, you may need to paint it, but it will have that 'personal' touch that will mean something to you for your new baby, and you can pick whatever color you want and add any personal touches... or you can resell it on craigslist if you really decide it was a bad choice or donate it and use it as a tax write off and consider it a life lesson that it's okay to pass on something the next time even if it means missing out possibly. Either way, it's a win/win situation... you just have to focus on the positives, not the negatives... I know it's easy to think this is something that just comes naturally, but you really can teach yourself to do this, even when you aren't 'feeling' it, I'm finding. It takes work and a lot of practice, but you can change your thinking here, you just have to keep at it.