I have a recurring problem with losing parts. Planning/designing a build is my favorite part of modeling. When I start anew kit, I gather all the parts I wanna use on it & put it in the kit box. Later on down the line, I can't find the tires & rims, etc.,to a kit I wanna start because I've so wisely planned another build with them! Did I mention I'm not real organized? This can be a bonus, too. I'm always finding parts I thought l lost! Sometimes too late though.