I dont know about any of you, but I eat tons of peanut butter while hiking, biking and typing this post. Okay, when you open a jar of whosever spread there a sealed inner paper to tear off the rim. Keep it and shove it inside the plastic jar. It will stay about 70% fresh about two opened weeks.
I use peanut butter plastic jars for keeping thing in I want dry, I use the jars in different sizes as cups and mugs, while hot to the touch a scorching ot to handle but they make great thermos's.
I also use a peanut butter jar to put jams and jellies in for that PB&J in the woods on pancake bread.