Strictly by chance, I found the Aquafina water bottles from the local convenience store fit my bottle cages perfectly, and snap into place and don't bounce out. Sure, they use a regular cap but since I do all my drinking while stopped, it doesn't matter anyway. It's no slower than drinking vodka from a bottle found in a dumpster.
I bought an Enve seatpost.... It's priced like you probably think an Enve seatpost would be, but it's gorgeous and the attachment and adjustment screws are really clever. I'm glad I bought it.
On the other hand, I bought a Spurcycle bell and decided it was a waste of money and returned it. The $6 bell from Dick's Sporting Goods is a lot louder and everyone recognizes it as a bike, which is something I can't say about the Spurcycle. I really think people hear it but don't recognize it as a bell.