It's really hard to tell if it'll be t-shirt weather or not. The temps in Las Vegas have been a little below normal lately, with daytime highs in the last week or so around 10 or 12 I think. It's also been raining a lot.
At night it's a different story. Las Vegas is in the desert, and strangely enough the desert is pretty chilly at night. You'll definitely need a jacket for the evenings. Night time lows lately have been as low as 0!
No real packing tips - Vegas is really laid back and most places frankly don't care how you're dressed. Some of the fancier restaurants will insist on jacket & tie, but for most places as long as you're dressed, you're fine.
My biggest tip for Vegas is to make sure you sign up for the player clubs at the various casinos. Excalibur is part of the One Club, which includes Luxor, Mandalay Bay, Monte Carlo and a few more. They sometimes give you incentives to sign up, like coupons for buffets and stuff. If they try to give you the cheap springy keychain - take it. Just once though. You can put all your cards on the one chain and they're easier to keep track of that way. Oh and just about every Vegas casino will give you 2 cards when you sign up - I think that's in case you lose one, or want to play 2 machines, or if you and your spouse both want to use the same account so that you earn points faster.
If you show your players club card in some of the hotel gift shops, you'll get a discount on your purchase.
Monte Carlo has a free slot tournament, it's run on the hour from something like 11-5 during the day. Get there early and sign up though, because they start taking names for the tournament an hour before the actual play time. You'll get a free gift just for playing (usually a key chain or a travel mug).
