It keeps for awhile. After a long period of time and some extreme temp changes it gets a little stale. I still ate it with no side effects. As long as the expiration date is still good, you should be fine. It might not taste as 'fresh' as the stuff you keep in your pantry.
I also love saving the peanut butter jars after they are empty. I wash them out and use them to make homemade first aid kits. They are tough jars, water proof, and can fit a lot. Plus being clear you can see what is in them. They are big enough to fit a lot of stuff crammed in or don't take up too much space in the pack. One in the truck bag, one in BOB bag, and two on my ATV bag (one first aid and the other fire starter kit).