The must-do if in Vegas is go to a pool party. We went to the one at the Encore hotel but I've also heard there's a good one at MGM Grand as well if you're nearer that end of the strip. There are some on other days of the week as well (to be fair most hotels have really good pools and music every day) but Sunday seems to be the main day for pool parties.
The Encore one was insane; I have never seen anything like it before. Afrojack was playing and everyone was dancing around in the water, drinking and having a great time. I had to pinch myself to check it was real. So sad to be leaving Vegas tomorrow! Next stop is Utah for a two night detox before we continue our trip to Colorado.