The perfect bag/box shape for the tool set will depend on how you plan to haul/store it. Mine is relatively flat on purpose, so I could quickly stuff it into side pockets of my various daily activity carry bags (car camping chest, scuba duffel, astronomy bag, IT rescuer wheeler, bicycle side bag, as well as to insert it into the special shelf opening in my work table at home.

By the way, a grab and go tool set should always have a minimal collection of materials as well, i.e. assorted screws, nuts, washers, wires, gaskets, ties, hot glue sticks, epoxy, glue, tape e.t.c. I'm also carrying some electronics components for rigging something more sophisticated when necessary (relays, voltage regulators, resistors, capacitors...).

Also, when the space permitting, I'm stuffing my box with the attachments/blades from older tools (like damaged screwdriver blades, chisels, razor blades). Using a torch and files you can make many specific to the task pointed tools or HD fasteners out of them in the field.