Neil D... I have mixed PB with honey. It spreads without being runny on bread. I have also seen a commercial brand of it, but didn't buy it. I do have some good maple syrup. Maybe I'll experiment.
    I wouldn't object to banana...just never bothered. Next banana perhaps... I use most banana on cereal.

There are some things listed above that I simply wouldn't try...such with mayo. Since my first PB sandwiches 80 years ago were with jam or jelly, sweet combos just became the norm.