I have to go out to Vegas a couple of times a year for work, here's my 2 cents:
On the strip:
There's a somewhat pricey place called Public House at the Venetian that has a pretty decent beer list, sometimes has cask offerings. Plus they have poutine, so that's a win. I'm not crazy about Ellis Island at all. There's a souvenir shop next door to MGM grand (it is Grand Canyon-themed) that has an ok selection of cans and bottles at not-too-unreasonable prices for the Strip. Since there are no open container laws, it isn't a bad spot to grab something to wander around with.
Since you're going to the Grand Canyon you will end up driving through Henderson - there is a ridiculous place out there called "Nacho Daddy" with fun Mexican food (Thai nachos!!) and a decent beer list. For a while they used to pour a black & tan using Arrogant Bastard and Old Rasputin that was awesome.
As far as local beers, I haven't found anything Nevada-based that knocks my socks off, but San Tan (from AZ) is pretty good, and you can sometimes find stuff from Kern River Brewing Co, which is generally excellent. Some of the larger San Diego-based breweries have a presence, and you can get Green Flash, Stone, and Ballast Point beers a lot of places. Dogfish Head 60 minute IPA is all over the place.