If I were getting a 50% equity stake, I wouldn't expect a salary. That's basically a cofounder role, and the risk/reward work out appropriately. I'd expect to live off my own savings - but I'd also expect significant input into the business, including the ability to change its direction if the original idea really wasn't working. Basically, if you give up 50% of the company, you're in this together, better act like it.
I might expect a relatively small (cover living expenses) salary if I were taking on, say, a 20-30% equity stake as a cofounder in a pre-traction startup. This is sort of a no-man's-land of risk/reward tradeoff, though. There's an awkward dynamic when you're paying someone else's living expenses and yet their salary is still well below market-rate. It's worked for a couple startups (Hotmail was one, Intuit may've been another, though the equity stakes for Intuit all got renegotiated when they almost went bankrupt), but you don't see it often.
Once you're down in single-digit equity stakes, it's expected that you'll pony up market-rate salaries. That's what fundraising is for. :-) The equity stake for early employees is there to compensate (and incentivize) them for the possibility that their salary may not be their tomorrow, not for the lack of a salary.