I build mostly semi trucks and rarely “out of the box,” so I usually have a ton of left over parts. I use a parts organizer like Bill pictured above for smaller parts. I separate everything; mirrors have a place, emblems have a place, grilles, etc. I separate other items in various size ziplock bags, from snack size to freezer bags. There is a bag of fuel tanks, a bag of wheels, a bag of tires, a bag of drive axles, etc. I keep the bags in semi truck model boxes. I also have a model box full of truck cabs, hoods and bodies. Some of the boxes are stacked under my desk, others are in plastic totes.