I've been beach combing for several years now. My collection of stuff is pretty interesting - hand blown glass globes used as floats for fishing nets,other floats of all shapes and sizes, sea beans, pieces of SpaceX rockets, lobster pot tags from Japan, pieces of plastic w Cyrillic, doll heads, plastic frogs... the ocean's bounty is limitless it seems. I even found part of a wrapped brick of Mexican dirt weed once.
This one didn't make it to the collection but I did pick it up to dispose of when I left the beach.
https://en.wikipedia.org/wiki/Drift_seed
Plant seeds from salt tolerant plants that wash ashore in various coastal areas.