If you are using ME, but taking your baggage with you, you pay the fee at the airport check-in.
If you use RAC, they will leave a notice in your room the day before with a number to contact "BAGS" via phone to pay the baggage fee with a credit card. You will receive all the instructions on how to check out.
Then you go to the RAC with your confirmation number that you paid your baggage fee and they will check-in your baggage and take them to the airport.
If you want assistance to get your baggage to the lobby, go to the guest services desk about three days before you leave. Ask them to come by about 30 to 45 minutes before you need to leave, if you are leaving directly to the airport after checking your bags. If you have time during the day, like I do, you can just give them a time to pick you up when you feel you will be ready to go.....