Minnows and baitfish
Minnows are the most common kind of baitfish, but it's best to use the type of baitfish a bass might find in its natural environment. Shad, shiners and sunfish are common baitfish that bass will go for, particularly largemouth bass. If you are going after smallmouth bass, it's wise to use small baitfish to make sure the bass will be drawn to them.
When you're fishing for largemouth bass, crawfish are a great option if the bass live in areas with crawfish, such as the south of the Minnesota-Wisconsin region. Crawfish can be difficult to fish with when live, but you can make good use of them by hooking them in the back just behind the head or by using a gang hook. You can also use dead crawfish if you prefer since they are easier to manipulate in the water.
Frogs are one of the toughest live baits to fish with; but if you use dead frogs, you can get a lot of effective use out of them. Hook the frog in the throat and let them get trolled through the water. Use smaller frogs and make sure to wait until the bass bites the hook; because of a frog's legs, you could get a few nips before one lands.
Some insects are great for surface fishing, and they're easily identifiable by bass. Consider dragon flies, nymphs and hellgrammites.
It's the most common and versatile type of live bait, and its value isn't lost on bass. It might not always get you the lunkers--baitfish are better in that situation--but a carton of worms won't let you down out on the lake.