When making decisions as to what to preserve, consider the simplest approaches first. The simpler the technology, the easier to preserve and retrieve the medium for future use. For example, books that "weather" the changes will be immediately available. Media that require electrical power and additional technology will be greater challenges to return to use, accordingly. For the longer term, CD technology will preserve better than magnetic-based media, which is more subject to deterioration.
The first step is to take an inventory of existing books and media on hand. You may want to make a decision as to what you want to preserve and what is not of such value. Make a decision as to what level of commitment you will make to the Library Project, which will be an informal, but serious worldwide project to save and preserve literature and other media through the changes. You need not begin at present to store-away these materials, but you will need stores of materials that will allow you to initiate storage when the time comes.
The simplest methods involve acquiring an inventory of good zip-lock bags, of various sizes, that will store all of the books and media you plan to protect. These should be stored out of sunlight, as UV rays will deteriorate the plastic bags. Also, storage of desiccant material is advised. These can be little bags of desiccant crystals or gel, available through packing and shipping supply stores. When the time comes, and you will know the appropriate time, you simply place a book or books into the zip-lock bag along with a desiccant bag that will absorb any moisture. You might want to single-book or double-bag your most valuable books. Books can be put into boxes (with protective packing, if you desire). If they are returned to bookcases, the bookcases should be placed flat on the floor with the bagged books secured within the cases (top and bottom with duck-tape). Extremely valuable books can be bagged and placed together in sealed 5-gallon plastic buckets. When packed together, they should be packed firmly enough together to avoid friction wear between the bags. There will be losses, using this method, just like there will be human losses. But if enough of us add preservation of a book/media collection to our list of end-time priorities, we will have a good chance of carrying the best of our present civilization forward.