Commercially canned creamed corn is made from corn kernels, water, salt and a thickening agent. There isn't any cream in it. The name may have been derived from the milk or white liquid that exudes from the corn kernel when it's cut off the cob. Creamed corn is used in soups and casseroles and as a side dish by itself or mixed with onions and bacon. What you substitute for canned creamed corn depends on how it's used.
Frozen or Fresh Corn
If the corn flavour is the most important factor when using creamed corn, then use an equal amount of fresh or frozen corn. Add the corn toward the beginning of the cooking process of the recipe so the corn has a chance to cook through. If you want to mimic the sauciness of the creamed corn, put the fresh or frozen corn in the food processor. Give it a whirl or two to break up the kernels. Add 1/2 cup of milk and 1 tsp of cornstarch. The cornstarch will thicken the juices released from the corn and the milk.
Use a cream soup in a flavour that complements the final dish. For example, cream of celery soup or mushroom soup would work as a substitute for canned creamed corn in shepherd's pie, a combination of seasoned ground meat moistened by creamed corn and topped with mashed potatoes. A chicken chowder soup would work for a dish that includes chicken. Some soups are condensed, which means you need to use half as much soup as the creamed corn and add an equal amount of water or milk. Otherwise, the dish may turn out too salty.
Cream sauce is simply milk, salt and flour. A thin white sauce is 1/2 tbsp of flour to 1 cup of milk, half-and-half or cream. Gravy consistency cream sauce is made with 1 full tablespoon of flour to 1 cup of cream. Whisk the flour into the liquid then heat until the mixture slowly boils for two minutes. Use the white sauce to replace the creamed corn when you don't need or want the flavour of corn.
Make your own creamed corn from scratch. Fry two chopped slices of bacon until crisp. Add a chopped onion and sauté over medium heat for three or four minutes. Add two cups of frozen or fresh corn. Sauté for another three or four minutes. Add 1/2 cup of milk or cream. Salt and pepper to taste.