I've got a friend who will put just about anything on bread with peanut butter. Except jelly. He can't stand that for some reason. He will actually get out two pieces of bread, but peanut butter on one, and jelly on the other, and eat them both. But if you give him a sandwich, he wont touch the thing. Anyway... he convinced me to try a few of these things....
peanut butter + bread + :
apples = not particularly weird, but I never would have thought to put apple into a sandwich. pretty good.
celery = very good, but hard to bite all the way through

cheddar cheese = very good as long as the cheese isn't warm
chocolate chips = amazing
chicken = strange. not really good or bad. i don't regret trying it but I wouldn't eat it again.
hamburger patty = very strange. better than the chicken, not as good as the cheese.
french fries = disgusting. I can't believe I let him talk me into trying it.
He's done a lot of other strange things with food, most of which I've been unwilling to try, but a few of them are pretty good. Cheddar cheese dipped in ranch is amazing (and I HATE ranch, I wont eat it on anything else). I think my favorite thing though, and you should really try this, take two waffles, toast them, then put ice cream between them and make a sandwich. Eat it quickly of course, since the waffles will melt the ice cream, but the waffles have to be hot or it tastes all wrong.