After 60+ years of modeling, I have a lot. I cut off the box art if it shows details or a finish I may use again & file it w/the instructions I may use again if I decide to make a conversion or wreck in the future. It's also helpfull if you want to get/purchase an extra sprue or specific part from the maker. The spares are sorted by type & country/period, like wheels, tires, ammo, clear, tools, spare parts, hooks, supplies, hvy weapons, MGs, hand weapons, kit, figs & fig parts, etc. for US, German, WWII, postwar, & modern.
Decals are sorted similarly in plastic zip bags, but in an old humidor w/silicate to keep them dry and safe from damage. I primarily work in one scale (1/87) and the two countries mentioned, so this is simplified. PaulE