The locals know all of the best wild Beach Plum spots, and clean them out before anybody else. I do not think they can be cultivated, but the plants can be bought. Very slow growers. However the rose hips from the beach roses (Rosa rugosa, a native of Asia) also make a delicate jelly.
We have a bunch simmering right now. Lots of recipes online.
Roses and apples are closely-related.