Pick your tube, container, or correct size Foodsaver bag if you want to go that route. If you look around, you can find various sizes of mylar juice containers. Starbucks sells 4.0 oz. Peter Rabbit fruit snacks, which are perfect. The caps are oversized, but I just snip off the silly parts with kitchen scissors.
Find a Monoject 412 irrigating syringe (ask your dentist for a few), and trim the tip with kitchen shears, a scalpel, or a sharp knife. Make the syringe opening as large as you can, but where it still fits into the opening of your container. Walgreen's has something similiar, for dispensing liquid baby medicines. They'll probably give them to you for free.
Warm up the expected amount of peanut butter in your microwave (only the creamy style will work for this technique, by the way).
Remove the plunger from the syringe. Use a Popsicle stick, or a very small butter knife, to fill the syringe. Squirt the peanut butter into the container, shake and tap it on the counter to get the peanut butter to settle to the bottom. This will be a somewhat arduous task, getting the air bubbles out and giving you room to add more peanut butter. I've used a chop stick to force the goo down into the container. You likely will need to rewarm the peanut butter by placing its container in some near-boiling water for a few minutes. Then shake and tamp some more. Eventually, you'll get all the air bubbles out, the container will be full, and you'll have a nice, light container of portable peanut butter.
I don't fully trust these fragile containers, so I place them in a secure pint size Ziplock for transport in my food bag.
It's a sort of messy affair, but you only have to do it once to supply yourself for a season's supply of peanut butter.