Well back to peanut butter etc., I suggest using those overripe bananas that are otherwise heading to the trash with crunchy peanut butter on fresh bakery bread. :banana:
Apparently Elvis liked peanut butter and bacon sandwiches. :elvis:
Pineapple on a pizza (in conjuction with ham) is not that bad and I prefer it to pepperoni, but my favourite is italian sausage and feta cheese.
Marmite is just too damn salty for a sandwich.
Using a toaster oven or perhaps a broiler, try thick sliced french (or similar) bread with a layer of parmesan cheese and a little garlic salt or powder for taste. Broil until the parmesan cheese bubbles, eat while warm.