i used to build stock car frames out of the used spruces. back in the old day when dirt track cars were hard to find, and before i found evergreen. most have got thrown out over the years. i used to cut up models and sanded the spruce were i would have half-rounds and glued them behind the seems. i had built a cherry picker out of some almost square spruce and some old air plane wheels. i looks a little rough, but what can you expect from a teenager. it is one of the thinss from my teenagers days that survives.
as for the extra parts i save them for other people that are looking for parts in my local club. they make great junk loads, bodies to test new paint on, extra bodies to cut doors out of to open other kits doors up.
the old boxes are used to store the parts. most of the boxes are sorted and many of the collections i have bought over the years are still unsorted, due to not having the time and room needed for sorting.
hope this helps. gerry