I've used two different options depending on how much I peanut butter I'm carrying (i.e., how long I'm out). The first option is any lightweight plastic bottle that seals well. For example, an 18 oz net wt plastic Skippy peanut butter bottle hold enough peanut butter for many days at 2 oz per day.
A second option is to package individual servings in 6.5 inch by 3.25 inch plastic ziploc snack bags. You can just cut off a corner and squeeze out your serving. Obviously this works best it you use up everything in the bag at one sitting. I usually use this method for shorter trips where I only have peanut butter on a few days.
It's a good idea to double bag your peanut butter container in case it gets hot and the oil tries to leak out of the primary container.