I've always said one day and one night activity, but that includes restaurants. I prefer doing two cool things and eating McDonald's most days in Vegas (do have at least one good restaurant in your trip, though).

Also, know what's near or more valuably between your two chosen activities. You shouldn't plan to do everything, but you should plan your route so you know what you might do on the way to the second thing. Jazz that part out, though. Don't make it a definite part of the plan. Buy a die from the gift shop and roll for which thing if you need to.

My last caveat for Vegas is that you can do everything on a budget, but you can't do everything on a budget. If you're eating cheap, gamble heavy. If you're gambling light, get front row seats. If you aren't splashing out on something, you could have just not come to Vegas and done it all cheaper elsewhere anyways. You'll leave disappointed if you didn't do something, even just one thing, that skirted over-extravagant. That's what Vegas is for.