I've seasoned and floured more chicken than I need to fry. What's the best way to store it for cooking at a later date?
There is no good way to keep it in the "ready to fry" state. I'd suggest to simply store it in the fridge as you would do with unfloured meat. When you take it out, just flour it again. The thicker flour crust will make it somewhat closer to a schnitzel, but it won't taste bad. 

If you already had a very thick flour/egg/flour layering on it, it's probably better to wash it off and dry with a paper towel before storing, then redo the panading procedure for the next fry.