That's what I call them anyway: they hold a panel (like an easel) and have a built-in palette. I started making them when I needed a 6x8 pochade box. Eventually Maddy (who had bought me my first pochade box) got me a proper box for Christmas but not before I had made good use of my lashed-up version. I wanted something really light that would take two boards and mount on a standard photo tripod. This is it - still in regular use. Of course it doesn't have anywhere to store stuff but sometimes that is actually an advantage.
Now I think of it, this is not the very first palette-easel I made. Eight years ago we had a short stay in Barcelona. I made a very crude palette-easel out of two pieces of marine ply, hinged using piano hinge and kept rigidly open by a piece of coat-hanger wire. I used it for several small acrylic sketches when we weren't being Gaudi-ed to death or rambling the Ramblas. I now keep it set up for very lightweight acrylics work - with formica sheet taped to the palette part:
My next effort was early this year. I built it so that I could use up all those odd-sized panels that don't fit in pochade box slots. With the two panel carriers of similar design I can return from painting with three, wet, odd-sized panels stored safely.
The impending Venice trip has set me off again on the quest for a very light, 'high-capacity' palette-easel: one that can take panels up to 14 inches high and 15 inches long. Here is my latest effort with a 16x12" board in place. I bought the marine ply in Lydney 37 years ago! The worst technical problem is making the screw-set that bears on the top panel gripper. The gripper slides in a channel at the back and has to be locked by pressure from the screw.
I reckon I could do better but I think I am getting close to the limits of what is achievable with a schoolboy carpentry set! The alternative is to buy a commercial pochade box - expensive but labour-saving and the good ones are very good indeed: the two that Maddy bought me 11 years ago are still going strong.