Rule #1: Don't EVER listen to DOMS. He's a fucking idiot.
The Rio buffet has a very large selection of different types of food............but they all SUCK. Walk up the Strip to the Paris. Much better.
Hoover Dam is a great attraction, but it's NOT 15 minutes away, it's about an hour. Well worth it though.
Valley of Fire is about 30-45 minutes North. Nice place if you enjoy hiking. Same for Red Rock Canyon except it's to the West.
The Grand Canyon is four hours East. Since you won't have a car, I wouldn't bother putting that on your list.
Tattoo parlors are everywhere. Just don't go to one in a casino. You'll pay double just because of their location.
From the MGM it's a five minute cab ride East on Tropicana to The Gun Store. You can rent revolvers from .22 caliber all the way up to .44 Magnum. You can also rent semi-auto pistols from .22 caliber up to .45 ACP. Or you can rent a fully automatic rifle; M-16, MP-5, Grease Gun, S.A.W., etc. (Ammo for the machine guns is EXPENSIVE though.)
Alcohol stores are everywhere. But your best bet is to find the nearest grocery store and get it there. Best prices.
The weather in December can be anywhere from sweltering hot to freezing cold. Best bet is to pack long pants and long sleeve shirts. Throw in a couple of sweatshirts and a light jacket and you'll be fine. Don't bother with shorts and/or t-shirts, if it gets that hot you can buy some cheap ones.
Last but certainly not least, prostitution is illegal in Clark County. (That's where Las Vegas is.

) If you find a hooker here you'll pay thousands of $$$, risk catching something you'll never get rid of, and also possibly land your ass in jail.
Any other questions just send me a PM. And again, DOMS is a fucking idiot. ( I just like saying that.

)