Fall clothes are appropriate. 70's during the day and into the 40's at night are normal in the desert in November.
DonDiego's recollection is that Las Vegas is not the most Christmasy city one could seek. Nonetheless, the Thanksgiving weekend is the start of the Holiday Season in Las Vegas, as it is elsewhere.
Lots of the buffets and some restaurants will offer traditional Thanksgiving comestibles.
Certainly the stores will be bedecked for Black Friday. Otherwise, it'll be like most places, . . . some decorations up, some not.
For example:
__The Ethel M Holiday Cactus Garden will be fully decorated for a visit by Santa Claus on 16 November this year. [DonDiego would prefer the jolly fellow remain at the North Pole working on gifts for DonDiego, . . . but he does get around in a sorta magical way.]
__The Bellagio Conservatory will still have its Fall Harvest Display up through 24 November; the Winter Holiday exhibit won't be up until 2 December.
Anyway, DonDiego says: "ENJOY!"