OP, if you actually wanted an honest answer to your question, I suggest reading Rich Dad Poor Dad. Normally, wealthier people know how to keep money within their sphere of influence. Money stays with money. The times that you see your fellow medical students splurge on a $400 alcohol binge, where are you? Are you in the same place drinking a $12 beer? Or are you quietly at home, quietly stalking their after-thoughts on Facebook? Just be aware that you only have one perspective. It may seem that there is an absence of financial responsibility to you, but to them, they justify every dollar that they spend, trust me.
I went to undergrad and became best friends with someone who came from old money. I have to agree with what /u/atomi said, because my friend spends every waking minute thinking of how to make money for himself, creating 3 successful and countless unsuccessful businesses. The money that he spends in clubs, he tells me, is always warranted. Each chance out is an opportunity to meet other wealthy people to network. At first, I had trouble accepting the fact that he literally has to "party" as a living, because it's essential for networking. But now that we've been friends for over seven years, I know that he doesn't even like it anymore.
He now does work in Singapore, and enlightened me on something that I was ignorant of. If you went to an international-friendly school, and you've seen Singaporean students driving M3's and GTR's, you might think that these kids' parents are irresponsibly splurging on their children. Well, in Singapore, you essentially pay around $300,000 to buy a Camry ($100,000 import license, and about $170,000 in import fees). Keep in mind that these are wealthy people, and they're able to afford $500,000 for a family car. When their children come to America for college, spending $80,000 on a car seems like a steal.
While it's not completely the same, I think there are parallels that can be drawn to your experiences as well. It's all relative, and all based on perspective. I implore you to just take a step back, and unless their actions are directly hurting you or making your experience in medical school any lesser than it should be, just chillax bro.