What I do for small rock or ornaments things like you mentioned, is put them in the toilet tank (reservoir) for two weeks. The constant flushing of new water will clean them up. I’ve done this and have had good outcomes. You can also do a vinegar or bleach bath followed by rodi soak for a few days.
If they were collected right off the beach I doubt much is needed since they belong in saltwater. As long as there’s no pests.