You would be hard pressed to find hard liquor in most buffets, but if you beg enough they usually can send someone out to get you one. Best advice for that is to bring it in if you want it.
Best overall value to eat at is the Palms IMO. The buffet and cafe are great deals, Gardunos isn't bad for Mexican (I am very picky on Mexican so hard for me to say any place is good), and the atmosphere is always "nice".
Orleans buffet is the best value, breakfast might be the best deal in town. Rio buffet is excellent, but long lines, not cheap, and the fact that there is just too much good food to eat you can't eat all you will want there. Bellagio is good for buffet if you are craving upper crust food and the desserts are good.
For drinking and eating, go to Pink Taco before 6pm, get two for one Pacificos and order up some tacos and you can't go wrong.
And the good ole dog at the Ho is now $1.49, but still a good deal. For $3 you can get a huge hot dog, 3/4 pounder, and a 27oz margarita that has a little booze in it. Where else can you get a deal like that?