Few soft-plastic lures work as well as a ribbon-tail worm does behind a Carolina Rig in the summer. I have a variety of colors and sizes I use depending on the water clarity and the mood the fish.
If I'm fishing clear water, I like to use a 7.5-inch worm in a natural color like watermelon or green pumpkin. If the water is stained or muddy, I opt for a 10-inch worm in either plum or June bug.
If I'm swinging for the fence and targeting big bass, I step up to a 12-inch worm. Make sure to have a variety of these in your tackle box for summer fishing.
There are probably at least a 100, or more, different creature baits available, with different appendages and profiles to choose from. I've found when I'm fishing one behind a Carolina Rig, I want it to have a lot of kick and vibration. Creature baits that have large thumping appendages seem to trigger the most strikes for me.
I will note, however, there are times fish want a more subtle, natural presentation, especially in clear water. When conditions are tough and the water is clear, I may opt for something like a beaver-style bait or a baby brush hog in a natural color.
When fish are keying on shad, I find a fluke fished behind a Carolina Rig is a great option. Carolina Rigs are great for fishing deeper structures, and we all know there's a time for slugging deep-diving crankbaits around ledges and points.
However, there are times fish prefer a more neutral presentation and, in those instances, I've had success with the fluke behind the Carolina Rig when they're not eating the crankbait well.
When I fish a fluke with a Carolina Rig, I like to use a long floating leader. This will put the bait just above bottom-oriented bass, and they can't help but eat it.
Back when the Carolina Rig became mainstream, the plastic lizard was a bait that shined above the rest and it still works today. It's a plastic that shines in the spring time during the spawn and post-spawn period.
During the spawn, a Carolina Rig lizard can be used to fish deeper beds with great success. Something about a lizard's profile still drives bedding bass crazy. It can also be used with great success during the post-spawn period. The smaller profile of most lizards work great for finicky bass that have just finished the spawn.
Don't be afraid to upsize to a larger lizard; they have caught scores of giant bass throughout the years.