We just had a thread on this. Lotsa bad info in this one.
All the old municipal ordinances (NLV, Boulder City) were invalidated by the state legislature in 2007. I have heard that some cops in those jurisdictions have yet to acknowledge this reality, but it is the reality. As long as you're legal to have the handgun at all, you may keep it in your car, loaded, open or concealed (you may not have the gun concealed on your person, even in your car, absent a valid CCW, but glove box, under the seat etc. is fine). Unless you know someone who lives there, I can't imagine why you'd go to NLV, but if you want to visit Hoover Dam (which is well worth a trip) you'll have to pass through Boulder City. The worst a cop could do, though, is hassle you, because car carry is perfectly legal.
You may not have a loaded long gun in your car in Nevada - fish & game thing.
Open carry is technically legal in NV, but it's by no means common here in Vegas. I cannot remember the last time I saw anyone doing it. Unless you're eager to be a test case (and to investigate the mysteries of the Clark County Detention Center), do not open carry in or around the casinos. I would expect to meet some police officers, if open carrying anywhere in urban Clark County.
It is perfectly legal to take a gun into a casino/hotel. (Again though, if you advertise it it's likely to become un-legal in a hurry. I'd leave the shotgun case with the "Kill 'em all" and "Peace through Superior Firepower" stickers at home.) It may violate the property's policies; I don't know anything about that. There are no conspicuous "no gunzzz" signs at any property I've been to. (Mandalay Bay, the Tropicana, and the Riviera have hosted gun shows.) Leaving a gun in a hotel room is no better an idea in Vegas, than it is anywhere else.
Nevada is very gun-friendly, but Bugsy Siegal and Tony Spilotro are long dead. Don't wave the things around. If you don't cause any trouble, your guns won't cause you any.