Seen this and thought it might be useful (thanx go to moggy for finding it)
Mussels and Razorfish
Mussels can be bought alive from fishmongers or frozen from bait shops and pet shops. Most housewives know to reject mussels that don\'t clamp shut when tapped but anglers need not worry about this as mussels which are \"off\" often make the best bait. Live mussels can be parted from there shells by severing the anterior and posterior adductor muscles and scooping out, or leaving to die in a bucket (helps bring out the flavour). Mussels are not on the menu normally as they are protected by a hard shell, those which are eaten have normally died and have been washed out. Tie mussels on to the hook with thread, taking care not to pull to tight. I like to freeze them on the hook and keep them wrapped separately until needed, this allows them to be cast further, they will defrost quickly once they hit the water. Adding pilchard oil to the mussel before freezing increases its effectiveness. Although the edible mussel Mytilus edulis is the one normally used as bait the horse mussels Modiolus modiolus can also be used. Other native species are too small to bother with. Mussels bought frozen pet shops are very small and make good lugworm and mussel cocktails. Mussel beds are also good places to fish.
Razorfish Ensis siliqua, also called pod razor and spouter fish are rarely for sale so have to be gather by hand. Walk along the low tide mark without shoes on very softly and look for keyhole shaped holes in the sand. Pour salt down the hole and grab tightly when it pops out. The smaller Sword razor is also suitable. Treat as mussels for bait.
Many species of bivalves can be found buried in the sand e.g. gapers, scallops, tellins, cockles, oysters, etc and are worth trying for bait where they are abundant.
Do not bother with limpets