Plastic Bag Jar Gasket

Peanut butter jars and similar jars aren't as waterproof as they should be. That's why people still buy expensive heavy plastic jars at camping stores instead of using the free lightweight ones they have at home.
Mexican fishermen know a better way.
All you have to do is close the lid over a plastic grocery bag.
The plastic bag forms an excellent gasket, keeping your passport, photos, lighter or whatever nice and dry.