Well, in college, I lived on one meal a day for some time. Meeting Street Café sandwiches at 3pm for the win.. : )

I was a pure math major. Getting a math degree from any major university (applied or pure) guarantees that almost nobody will wonder if you're intelligent.

Past that, applied math -> finance seems to have been the most lucrative path for people in the '90s. I'm not sure what the current situation is.