Unlike other airports, I can come about an hour early with time to spare to get to my terminal. One of my favorite things about Mccarran. Make sure your ID and passport are in your hand and ready to go as you walk up through TSA. Be aware of what you can and can't bring on the airplane. After that, it should be smooth sailing.
If you are early to your terminal sit at a bar and have a drink, grab a bite to eat, or test your luck one last chance with the slot machines (yes slot machines galore throughout the airport).