Like, hmm, if you can’t refine oil anymore, how would you set up large-scale ethanol production so that you can run engines? How would you modify the engines to run on 100% ethanol? Where do you find ore and how do you smelt it? If you want to make gunpowder, where in the world do you get saltpeter and sulfur? How do you make gunpowder, or even just charcoal, without blowing yourself up? Can you make hormonal birth control, or even condoms? How about antibiotics? I’ve had some very good wikiwalks starting from questions like these.