Since it been 14 years from your last visit
In no particular order:
1) Go downtown (Freemont Street) at night. Walk from The Plaza to the Flaming Praying Mantis. Weekends are best.
2) Poker in Aria is very nice but Beligo has the best free drinks and a great room.
3) Climbing, scrambling or hiking in the Red Rocks is a must (off Charleston on 20 minutes from the strip)
4) Shows: KA & O are excellent
5) Food: endless choices if you like it fancy bring a lot of credit cards.