If you are BA gold fly AA you should get priority check in at LAS and free luggage though if you are flying FC you would already have that

look up your flight on flightaware prior to checking in your bag make sure the incoming equipment is there or in flight and on time, once you hand over your bag your flexibility to change flights is greatly reduced if you haven’t checked in your bag and if your flight is delayed or canceled just buy a ticket on another airline you have plenty of options and can get a refund for the unused ticket