Anyone know if there's a case or wallet on the market to hold a packet of Jumbo cards? Or perhaps some sort of case/wallet that is made for some other use but can be repurposed? I can't seem to find anything. Thanks.

You might try a sleeve for a Kindle reader (the simple sleeve protectors, not the type that opens like a notebook). I just tested mine - jumbo cards will protrude slightly from the top, but that might be a plus if you want quick removal during a performance instead of fully-covered protection. It will hold a few jumbo cards nicely, but if you try to shove half a deck in there, the fit will be too tight. One caution - Kindle readers come in more than one size - The sleeve I tested was for a Kindle with a 6" diagonal screen and a body of about 4.5" by 6.5".

Dollar Store solution: plastic folders that students use for holding papers together. Cut to size and tape with electrician's tape or color vinyl tape on two edges (or on three edges just for symmetry). The top can be a fold-over top, or a separate piece taped to the back so it folds over, and can be tucked down inside like a card box, or it can remain on the outside and stick with a spot of double-sided tape, or some Velcro tabs.

Thanks Emory & Jim! Interesting ideas to explore.