Frozen bait can be bought, but avoid it if you can, it tends to lack the scent and texture of fresh bait. Impact sheilds are worth including in your rigs, particulary if you are distance casting. They protect bait from the force of hitting the water. Just clip the hook behind the shield before casting. A combination of two baits often catches when a single bait doesn't.
Lugworm is probably the most popular sea bait.
It will catch most types of fish. Aberdeen hooks are best. Slide right the way onto the hook. Notes Live on foreshore, and can be dug using a fork at low tide. Lug can be used in any number of combinations, but notably with either squid or peeler.