I ordered one from Nutztogo.com and it fits my Brita perfectly. In fact it would probably hold one even a little bigger. It has a small zippered pocket on the front of it that will perfectly hold AP, CC, DDE card, room key, and a little money. I think I paid about $7.00 for it, but I'm not sure.
If I need to carry more 'stuff' I plan to unhook the neck strap off the insulated carrier, put a multipurpose tie through the key chain part of a carbinger clip, zip the tie tight around the neck of the Brita bottle, then use the carbinger clip to make it easy to clip it to my fanny pack or back pack. In fact, I already have the bottle rigged up with the carbinger clip.