I would honestly say, "What can't you cook in cast iron?" Not a whole lot, actually.
Ice cubes, lemonade, and microwavable meals are not made in cast iron.
At first I thought tossed salads, but sure you can toss salad in cast iron.
Hollandaise sauce and custard should be cooked in a double boiler. There are no cast iron double boilers. Possibly you can rig one, by placing the Lodge 2 quart serving pot inside the 5 quart dutch oven with boiling water.
There are no cast iron "turkey fryer pots." Unless you can find a 26 to 30 quart slender cast iron pot*, you can't fry turkey in cast iron. You can, however, roast turkey in cast iron.
*I found a 28 quart cast iron pot online, but it's short and fat. Turkey pots are tall and slender, so as not to waste expensive peanut oil.
I would not boil water for drinking purposes in cast iron, due to the seasoning dissolving into the water. So iced tea and hot cider would also be out.
Boiling a sack of crawfish requires a minimum 80 quart pot with basket (or 2 batches in a 40 quart). They do have cast iron pots of that volume, but not with baskets. Possible, maybe; Practical, no.
Cooking tomato-based dishes in cast iron is controversial; Some say it gives the food a metallic taste. I've personally never had a problem.
From scratch tomato sauce, using fresh tomatoes, is an exception; It's recommended to be cooked in stainless steel. I start in stainless steel and then transfer to a crock pot.
While cast iron is not normally considered for steaming*, or cooking pasta or rice, sure you can**.
*There are no cast iron steamers. You can steam by putting broth at the bottom of the pan with the food, bring to a boil, and cover. A rack is nice if you can rig one, but not necessary.
**I normally steam, and cook rice, using chicken or beef broth, in a rice cooker.
Boiled peanuts and dried beans, both can be cooked in a cast iron pot, but I use a crock pot*, since I cook them overnight.
*Anything that can be cooked in a crock pot, can be cooked in a cast iron pot. But it's not necessarily the other way around.
If I figure out anything else, I'll let you know...