I use dried fruit, much less messy, you don't end up sticky. Raisins work very well, chopped dates are quite nice as well but a pain to apply so I generally buy whole dried dates and halve them. Sliced or chopped figs are quite good, apple rings are fantastic. Mango work fairly well as is but sometime are a bit tough, chopping is often a good idea. Chopped apricot is a favorite, cranberries were a disappointment, pineapple works well as does fresh chopped pineapple as long as you let it drain a bit before putting it on your sandwich. Sundried tomatoes and fresh sliced green pepper is better than one would expect.

Some good thin potato chips are a great way to add some crunch, I prefer Old Dutch Original, great on many sorts of sandwich.