I added $500 cash at checkin at POP and agree it does go very quickly, when you're just swiping a card!
I added more when it got low and then tried to carry a small amount of cash everyday and put tips and a few bigger purchases on the room. When I checked out there was a small credit balance and I got this back in cash.
Whether you do cash or link a credit card to your room key, you can request a print out of your account at anytime to monitor what you're spending and I found that useful at the end of everyday to 'balance' my spending.
DD and I are there in 2 weeks and I plan to do a mix again, cash in a chunk on the room and then take a small amount of cash with me. This way I dont have to carry lots of cash, but aren't worried about running up a big credit card bill! DH would kill me! lol