The idea:
A building where you can put all your excess junk in for caravans to pick whatever they want out of on their way out of the map. No bartering necessary; when they get ready to leave, they stop by the gift box and fill up as much as they can carry with free crap you don't want.
Why:
Replacement for atom smashing/tossing things in the magma sea. Easy way to get rid of unwanted items, only this way, you get exported wealth too.
Ideally the gift box would do the following too:
1) Items within would not calculate temperature or any of the other things that cause FPS lag with large amounts of items. This is, after all, the main point: to replace atom smashing.
2) Not allow you to take items out of it after being placed in. For all intents other than this, the item(s) were atom smashed. Presumably the items are completely gone if the building is destroyed.
3) Give you exported wealth instead of nothing.
4) Make it so you don't have to bother with bartering if you want to just give merchants stuff.
5) It should have an easy way to designate things to be tossed into it (rather than the current dump command).
6) Merchants would take things they otherwise wouldn't (elves would take wood to give it a proper burial or something, others would take stolen goods to return them, etc) but you wouldn't get any exported wealth for it.