Shrimp and bits of squid will catch spot, but not as well as bloodworms. Bloodworms are expensive, but there's a reason for the cost. They are saltwater marsh worms that grow to several inches and live among the saltwater marshes of New England and Canada. Each worm must be harvested, packaged, and then delivered along the entire East Coast. Bloodworms are hardy, but will die quickly if left out in the sun or allowed to soak in fresh water, so don't let them fall into the water at the bottom of your cooler.
Most coolers come with a small tray that fits on a ledge near the top of the cooler.
I leave the worms in the little plastic bag they come in from the tackle shop. When I'm fishing, I only cut up one or two worms at a time, as I need them. Use only small pieces of worm, just enough to cover the end of the hook. One good-sized bloodworm should yield several spot baits, and it's not necessary to put a fresh piece of worm on every time you bring in your line. A fresh worm is necessary only when the hook is bare.