Almost everything should be recyclable.
Glass should be recyclable like metal producing raw glass, which should be usable in place of sand in glass object production. Historically glass was traded as ingots in classical antiquity.
Wooden objects should be able to be converted into charcoal based on size storing fractional bars in the furnace in the same way smelters store fractional metal bars from melting.
Quilts should be possible from worn cloth items and dwarves should use them to upgrade the quality of their beds. Rag paper was promised at some point and is also a good idea, but quilts are another way worn clothing has historically been recycled.
Bone objects should be able to be ground into bone meal fertilizer at a quern or millstone.
Anything organic should be able to be incinerated in a furnace to produce ash (plus fuel ash, so burning something like a bed would take a log and produce two ash (one for the log, one for the bed) while burning something like a xquiverx would take a log and produce an extra fractional unit of ash in the furnace for the xquiverx).
Rock objects should be able to be turned to gravel that can be used directly for paving roads, in reactions (probably at 3 gravel to the stone since a bunch of crafting processes produce 3 products), and mixed with quicklime to make concrete.
Pottery shard were used in antiquity along with lime to produce early hydraulic cements, but I'm unsure if DF is ready to support construction from above in a way that would make hydraulic cements useful.
Merchants should not accept anything of xqualityx or lower. They're the least annoying way to dispose of xcrapx, though, so manager automatable recycling chains are kind of needed first.