It's almost impossible when you have 5-7+ studies but I've found having a system in place where all the info is easily accessible to be helpful as well as knowing which documents to refer to when you receive those emergency calls from site (documents common to any study such as protocol, CMP, etc). There's nothing worse than having a call from a stressed out SC, which then stresses you out, and then having to comb through lots of folders trying to find the right document while dealing with everything else.

As others have said CTRL-F is your best friend and having things like the CMP, Protocol, CCGs, pharmacy manual, vendor manuals, other SOPs saved in a place where you can easily and quickly find them.