I find the upcycling of downstream waste into viable products incredibly compelling: here’s [Tidal Vision](http://store.tidalvisionusa.com), which takes salmon skin from the Northwest fishery and turns it into leather that is then made into wallets.
I remember also talking with a local architect about taking rice hulls and mixing it with concrete in order to produce a building material that was both rigid but also, thanks to the hulls, lighter than regular concrete and with air pockets to increase its insulation value. I believe he was also interested in rice straw bales as building materials, but I think the problem there is that farmers typically don’t bale that material, but rather combines return the chaff back to the fields to compost.
I grew up in the land of sugar cane, and I remember seeing bagasse turned into garden mulch, but I think now it is mostly burned to power the mills where the cane is processed.
What’s leftover these days that could be still useful in some fashion? That strikes me as an opportunity.