You can get inflight drink chits either in the 1K kit or buy them at a slightly discounted rate at theunitedshop.com. That being said, FA's typically accept the RCC drink chits, because they can hardly tell the difference. I have never seen FA's turn them down, so definitely worth a try.

The difference is that the RCC's ones say "Redeemable in Red Carpet Club only" at the bottom.