The datacolor spider checkr are very affordeable and widely supported. But they are made of some kind of cardboard. So it was allways a hinderance to put it in a backpack or to put it on the tablet holder.
I liked the casing of some of the cheaper ones, but their colors are not useable in my workflow, and their plastic grid could cast unwanted shaddows on the patches.

For that reason I've designed and printed a simple frame (so you can use both sides of the chart) and two plates wich keeps it secure while traveling with the help of rubber bands.

You need to print the two files twice, and glue the frame together with ca glue. Putting the chart into the frame is a bit finicky due to the tight tolerances.

If you want to make the case fully closed, you are free to do, I release it under cc share alike.

Btw/edit, I tested a few cheap tablet holder, and currently I'm leaning towards the Ulanzi LT 29  (as I noticed LT-29 if you want it from another vendor) for several reasons:

It can be retracted to a very low profile The smallest in my collcection
It has 1/4 screws at the back and bottom
The spring loaded arms can be also adapted to various sizes (Images shows arms at various "expansion" settings) So it can adapted from phone to tablet sized objects
It cost around 5- 10 bucks if you do a little hunting.
The slotshave a relative low profile / casts little shaddow on the object which is clamped in.

The downside is that it is made from plastic and I'm currently don't have any reliable longterm experience  how well it last. And no I'm not affiliated with ulanzi. It just happens to be the second product I actually like from them.