It won't be long before this thread becomes about peanut butter. So before that happens I would like to contribute that there are a number of jams that go wonderfully with peanut butter. The science may not exist to prove why the taste combination of peanuts and smashed berries goes so well together but it appears to be a culinary constant. Now the real question is, while there are a number of different types of jams, going from strawberry, raspberry, blackberries, and any number of combinations with other common drupes, there are some that depend on taste. For example, blueberries. If you don't like blueberries, a blueberry jam and peanut butter sandwich will not be your favourite, regardless of how intense your love for peanut butter is. Also some people who do like blueberries detest the fact that in order to create blueberry jam it is necessary to add synthetic pectin since blueberries don't contain quite enough of their own. But I suppose that depends on their viewpoint on artificial food additives.
Apple jam, on the other hand, while still requiring a proper affection for it's flavour, and while not going with peanut butter quite as well as berries, is one of the highest pectin containing fruits, and thus requires no synthetic pectin.
Bananas, a natural companion with peanut butter, while traditionally simply served via slices on the bread alongside the chosen form of peanut butter, can also be smashed in much the same format as berries to create a gooey yellowish white mass that tastes of bananas and is easily spreadable.
OK. I'm done now too.