Garbage. How do you take a bag of mixed garbage and perform a fractional distillation of it, pulling out components and recycling and reusing them efficiently, until you are left with a tiny residue, ideally nothing, of true waste? How do you do this in a cost effective manner without relying on absurdly cheap labor and lax health, safety and environmental protection regulations?
Sadly I have but one upvote to give, because making that kind of optimal use of garbage would solve a bunch of other problems.
And it's like, purely a technical business. If you have a company that can "buy" garbage for $X and sell your outputs for $Y > $X (+costs), you don't need to deal with politics and lobbying and building buzz.