Two weeks ago I bought a gallon of pickles, because I thought: Oh, that'll last me a while and its only $7 and I can use the jar for something after. It did not last me a while, but I can still use the jar IG. The only remaining decision is what for? My thought is to store beans in it (so that the beans don't have to be stored up high to be away from mice and so I can do a custom blend more easily, and then if I got a second gallon jar (of pickles or otherwise) I could use that as a dedicated bean soaking vessel, which would make it easier to remember to get beans soaking) or use it for making/storing lemonade (tight sealing lid makes the mixing easier, I can just shake it.) But I wasn't just going to commit to something without asking for recommendations.
Before you ask, no, there's no chance I'll use it for making pickles, I would never want to make that many at a time (though I definitely will get a smaller pickle jar for making fridge pickled onions).
You could use it to store utensils next to the stove, or get some orbeez and make a fake aquarium. Also great for storing stuff in the craft/hobby space or garage.