Gluing the frame together using the elegant custom clamping/roping techniques that my paltry toolset affords. A good time to make sure everything is straight, 90 degrees, etc. No nails used in the cajon, just glue. Given the way the boards meet, it's plenty strong enough to hold the player.
 

Gluing the frame into the cajon. Due to slight errors in measurement and cutting, the frame pieces were a bit short; thus slivers of hickory were inserted to fill the gaps when the gluing was done. Note the custom clamp improvisations and the stacked wood and old paint can for bracing (tip: pink is usually the heaviest). Clamps would have been a lot better and easier, obviously. The image on the right shows the back side, where the door will be. Only two hickory pieces are required there. Hopefully it can be seen that the door will set flush against those two pieces and the two edges of the side walls. The overlipping top and bottom prevent shearing stress on the hinges from the player sitting on the cajon.