Not a lot of option for crabapples really. make a pickle - for cold meats its really nice and tart - make a glaze for hams; use in a savory bread; use in a cider cake, or make your family pucker up and add a couple to a nice apple pie for extra bite....
Marrows - food of the gods - stuff with celery, peppers, tomatoes etc and roast. Bake it, fry as fritters, make a marrow jam (with added ginger for some zing), make a curry with it, make a soup - use good firm beans, loads of strong stock and herbs - good hearty stuff! Or add pork knuckle for a meaty taste.
Add to breads; chunky pieces go well in stews and casseroles. Goes well with other veg like roasted fennel, carrot etc. Use it as a 'filler' on a plate - takes sauces really well.....cook with diced smoked bacon or ham and make up as a sauce for noodles....
Make a veggy crumble, make a veggy pie with a nice parsley cream sauce. Use in a tomato and marrow gratin as a side dish for roasts.
Dice, fry, use in pasta with tomato and onion - marrows are courgettes on steroids (or put another way, courgettes are marrows before their time...) , so anywhere a courgette is ok, using a marrow is generally ok too....
Hope that helps..