Update: 10/9/2018

A large update:

The existing design has been relabeled as "unsleeved_promos". After checking, there is enough room to store the promos currently available in the insert. If you downloaded the file already, it will work as is for the promos and unsleeved cards.
There is now a split version of the unsleeved insert available for printer with smaller build platforms. Print LH and RH and you can adhere them as you see fit, or leave them loose in the box.
After consulting BoardGameGeek about the sleeves that fit Sushi Go cards, there is now a sleeved card version that also supports the promos. It should accommodate sleeves up to 62 mm by 93 mm. Look for the "sleeved_promos" file.
Lastly, a split version of the "sleeved_promos" insert for smaller printers. Print LH and RH and you can adhere them as you see fit, or leave them loose in the box.

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After purchasing Sushi Go Party!, we started taking it places to play with people. I quickly found the stock insert lacking, as it didn't keep the cards in their slots. I'd have to sort everything out once we got someplace.

I decided to model up a new insert that would keep all the cards in place during transport, so I wouldn't have to sort them. I also wanted someplace to put the pawns during transport.

Modeled up in Inventor, the design went quick. I even included labels for where the cards go. I printed a sample print to test the fit with cards and pawns. A few tweaks needed from the prototype:

Making the pawn spots larger
Adding handles to lift the insert out
Lowering the card slots to make room for the board and manual
Widening the slots so the cards angle a little more.
Adding a cutout on the bottom to reduce material needed.
After those were all done, the final design went onto the printer.

I'm very happy with how it turned out. It fits well, the cards no longer come out of the slots, and I no longer have to sort them. I may make an improvement to the way the pawns are secured, but that's for another day. Time to go play some Sushi Go Party!