You CANNOT charge gift cards to your room card. I tried this on 12/6 to buy a $75.00 gift card to get the special gift that came with it only to be told that it cannot be done via room charge. I then gave the CM my debit card and purchased the $75.00 gift card. You can use any other form of payment such as credit card, debit card or cash.
Having said that, I put my debit card on file and do 99.99999% of my purchases on room charge. That way I have an itemized bill at the end of the trip of all of my purchases with an exact total of how much I spent. If I were on a budget, which I never am lol, then I'd check the folio charges daily when you return to your hotel to see what your balance is. I just got back last night and I can tell you that we spent $627.44 for our 8 days trip to AoA and did all the signature dining places and brought back a suitcase filled with souvenirs.