I had a nice time in Las Vegas in late February (21st to the 28th). The resort, Tahiti Village, was very nice, and I saw a lot. Also came away with some suggestions. Perhaps you can benefit from these random thoughts.
1. Take along 1st class stamps. You’re bound to find larger post cards, especially in the resorts. Those require 1st class postage. Perhaps your resort has some on hand to sell (mine was out on that particular day). If that’s the case, and you can’t wait until they restock, you’re forced to go searching. The post office is somewhere on the east side of town, so I headed to the Strip for an alternative.
One hotel, whose name escapes me, sells stamps through a small vending-like machine. They charge $2 for two stamps. Now, I realize that I shouldn’t quibble about prices while in Vegas, but I found that intolerable. I needed five stamps, so I moved on.