After 34 years in critical care; I never went to work without my own favorite med book, my stethescope, scissors, 2 hemostats, a penlight, my own 2 pens, and a critical care pocket reference book that I added my own paper to so I could add my own little "perls" to: I would add certain MD's odd little quirks (ie: if one surgeon liked some different lab test done that others didn't); hosp. and MD telephone numbers for emergencies; and if there were certain tests that were difficult to remember how to do them.
In other words, my extra pages of perls were the things I didn't use often but if I needed to use them I could find those things STAT.