I learned a couple of things that every prepper should learn. First, limestone is some good stuff to have on your property. Second, you can harvest some useful substances when you burn wood.
I am currently on the chapter of Advanced Chemistry and the section on explosives. It is slow going because I take notes and look up things as I go, but it is amazing all the things we take for granted. It is incredible how much we are going to have to do to rebuild post-SHTF. Better prepared and knowledgeable though.