The best thing you can do in that circumstance is charge everything to your room and use your (MGM or Caesars) credit card as the card on file for the room. That way you know you'll earn credits for the initial spend and then additional credits for using your credit card on qualifying purchases, if you use that card to settle your bill.
What if I have an MGM credit card or Caesar’s Credit card? Do I need to charge to the room or provide my players card number?
The best thing you can do in that circumstance is charge everything to your room and use your (MGM or Caesars) credit card as the card on file for the room. That way you know you'll earn credits for the initial spend and then additional credits for using your credit card on qualifying purchases, if you use that card to settle your bill.