Sometimes the foam cutouts are not practical due to available space versus number of tools, so I would suggest a thorough inventory on a list of some form, or a photographic record of inventory. Then mark the toolbox compartments with the total number of tools stored in that area.
That way, after work is done and the tools have been cleaned, as they are packed away they are counted and the total compared to the actual recorded total. Any difference must be investigated before departure.