Good outlet shopping to stock on clothes / trainers etc. The fountains at the Belagio (sp?). The roller coaster on top of the building. The lions at the MGM. Cirque du soleil wherever they're playing = amazing.
Er, 1 cent slots to keep the fun, but not lose all your money. Not a gambler myself, but they were pretty fun.
Which hotel are you staying at? Are you on the strip?