Jump off the Stratosphere Hotel skyjump (you can see vids on youtube)
Try to spend at least one night in the Luxor facing the airport, watching all those jetliners shoot up past the Mandalay Bay hotel is great, like a personal viewing gallery. For that matter take a walk out the road and watch them descend right above you.
Other than that, do the Grand Canyon tour and visit the skywalk. I went on the bus which was cool, apparently you don't get a lot of time at the canyon on on the chopper.
While not quite San Diego Zoo there is a Shark reef at the Mandalay Bay which is worth a look
and a shooting range where you get to fire live ammo
Other than that, visit as many of the theme hotels as you can and hit the clubs.