It's not always entirely ethical to produce Nintendo-themed goods and sell them on something like Etsy, especially if they're a straight-up copy of official equivalent art or goods. In the era of 3D printing, though, you can download files from fellow enthusiasts and print goodies (for your own use) at your own cost; it's a fun way to make yourself some custom gear.

A good example is this Question Block Switch Cartridge Case, which will hold some of your games and even spare microSD cards. You can see it below.

If you have access to a 3D Printer, this could be a fun little project to try out.

[source thingiverse.com, via tinycartridge.com]