When I began working on my Circus Layout I bought two aluminum briefcases - one to put the layout into and one to place the power supply, trains, etc. into.
While down in Monroe looking around at Jo Ann's fabric store I found a two-inch thick piece of polyurethane foam that looked like it should fill the briefcase with no problem, so I bought it. At home I cut it to fit into the bottom of the briefcase. My intent was to cut out spaces for the power supply, leads to the track, a screwdriver, and the rerailer ramp in the left half and then to cut out spaces for boxes for the trains in the right half of the foam.
I tried to cut the polyurethane foam with my Woodland Scenics Foam Knife. But the two-inch foam was just a little too thick to cut all the way through easily. I did use the Foam Knife to cut the slots for the wire and the rerailer ramp. To cut the foam to fit the briefcase and to cut out the foam to accomodate the power supply I used a kitchen carving knife.
After I got the left half done I realized that while individual engines and cars come in similar sized form-fitting boxes from Micro-Trains, that was not necessarily true for Marklin trains, where oversize boxes were the rule, and odd shaped boxes were often used for special cars. So cutting the foam for a "one-size-fits-all" pattern wouldn't work. Instead, I simply cut the foam in half and removed the right half. Now boxes of any size can be placed into the space and, if necessary, I could cut the left over polyurethane foam into appropriate sizes to keep the boxes from rattling around.
You might notice from the picture that I have left the pockets in the top of the briefcase intact for the time being. They provide a little padding on top of the items in the bottom, and they may be useful if used as intended. I can always replace them with a piece of one-inch foam in the future if they turn out to be more bother than good.
I would recommend the following items to be kept in the briefcase: power supply and power leads, rerailer ramp, small screwdriver (for attching leads to the power supply), jewler's screwdriver (for moving hitches into proper positions when the train won't hitch up just by pushing the cars together), small flashlight (so you can see the hitches and derailed wheels in less than ideal lighting), extension cord.