Whey protein powder added to peanut butter works very well - you can adjust for consistency and spread on whatever you like. Better control over the ingredients than purchased bars. For crunch you can't beat WASA crackers. Light Rye or other variety without seeds / lower fiber.
And if you are ok with honey, and can tolerate wheat germ, which works for me, I used to make these peanut butter balls for my kids' lunch boxes - many many years ago now. I've not experimented but pulverized oatmeal (a few pulses in food processor or blender) is probably a good substitute for some or all of the wheat germ and whey protein for the dry milk.
1 cup wheat germ
1/2 cup PB
1/2 cup honey ( can use less)
2 T dry milk
You combine, roll into balls, and keep refrigerated. Lots of protein. Very filling. Now that I think about it, will try a batch myself! Will probably use half the honey and roll in powdered sugar and cinnamon.