This is a photo of part of the shelf contents in back of my desk. I haven't read them all, of course, but I know what is in them. I believe its good to keep things handy that cover several levels of detail more than you ordinarily require. That way you can dig further quickly if the need arises.
There are a series of directories on the computer with everything I can find on manufacturer's literature, catalogs and manuals. If I know I'm going to need it to fix something, I print out the manual. If not, a copy of the files are always available on the truck computer. Occasionally I need to get on the web from the truck and hunt up something that became available after I last sucked everything off the manufacturer's site. I use a Verizon wireless card which gives me a good signal throughout my service area.