Snap-on a twist-on milk cap.

Image by Dan_H via Flickr You know the plastic jugs of milk that have the plastic screw on caps, not the snap on caps? (I prefer those because they actually stay on if you drop the milk and they're just much more durable.) Well, you can easily get the convenience of snapping them on with just one solid smack, however since they're threaded they need to be twisted just a little bit after the smack. This is easy to do with your thumb on the hand that you are holding the milk jug with and can be done simultaneously while putting it back into the fridge.