I ended up making bigger tubes than I had originally intended. Peanut butter was not very cooperating. Jelly wasn't too bad.
I tried putting a bunch of PB in a ziplock and cut the corner to make it like a decorating bag, then squirt it into the tube. Worked well until the PB prevented excess air from escaping.
Ended up making a tube, folding open end down to keep it as clean as possible and using a knife to pack each tube.
I'm sure I have more than I need in each tube, but I plan on splitting each one with my son while we are out. We'll see how it works…
Next time I think I'll plan a little better and find some prepackaged PB & J. Something along the size that comes in MREs would be great.