There are several starbucks located throughout LAS airport gates. The line is always LONG in the morning time. I know people want to get a cup of coffee to wake them up but god, they need to have more staff in the morning hours to fulfill the duties!
Tip: If you are not buying drinks or you can consume quickly. Try to buy your drink at the location before you hit the security. Its almost no wait over there and avoid the morning rush hour if you can.