Green Spout Water Bottle Adapters are one of the best inventions that no one has ever heard of! It's a little adapter you can add to a regular old water bottle to turn it into a sippy cup.
We first heard about these right before we went on a family trip to Disney World a few months ago. We carried around on-the-go packets of Crystal Light, mixed it up it the bottles and the kids would drink all day long! Perfect for keeping them hydrated.
I use these things ALL. THE. TIME! They are perfect for trips to the park, car rides, around the house, etc. They are small enough to stick in my purse just in case we're out and need to grab a drink. Since they don't allow any air to escape it will sometimes cause the bottle to collapse on itself, but it's easy to just squeeze the tip and let the air back in.