One of my favorite ice fishing items that I use is actually not a product designed for ice fishing. It's a tool box. Specifically, the Plano model in the pictures. It's got two detachable plastic boxes on top. I use one for my jigging raps and pimples and the other for my tip up lights and other accessories. Inside, there's a removeable tray where I store a couple of jig boxes, pliers, mouth spreader, leader material, church key, flashlight, etc. And, if properly stacked, I can fit 6 Beaver Dam tip ups or a couple of 24' panfish rod combos underneath the tray. It's kinda like my wife's purse, only for all of my ice fishing stuff.
A couple of other random but handy items that I can think of would be a bump board (Frabill makes a nice one that extends for larger fish) and colored marker buoys.