These are the Pochade Boxes I currently use. The larger one is a Guerilla Painter cigar box that uses 8x10 panels. It will store 2 hardboard canvas panels or 3 gessoed masonite panels (1/8"). The only drawback to this box, for me, is that you can only use the panel in the landscape (horizontal) position. It is possible to lean the panel in front to paint a vertical composition but I need to devise a way to keep the panel from sliding side to side. This is my main box and I even use it when painting in the studio set on a table or on a tripod right next to the easel.
The small box is a 6x8 Utrect Thumb Box made by Jullien. It will only hold one panel in the lid but will hold an 8x10 panel in the vertical position. This box is so small it's easy to throw it in a backpack or a bag on my bicycle. It does not have a tripod mount but has a thumb hole in the bottom. This is a real minimalist kit but still has everything I need as I use a limited palette of 4 colors plus white.
