I carry my Olympus E-5 paper manual in my bag when I shoot. I can't tell you how many times a new fricken' icon shows up in the viewfinder or on the LCD screen and I have no idea why it's there or what it means, or how to get rid of it.
My last trip was in October to Israel & Jordan and I took PDFs of every digital camera I have on my tablet - just in case I needed to look something up.
When I use Olympus TTL flash I put the camera in P and chimp the screen after every shot.
If RD, IIIf RD M3-Mot M4-P Contax IIa BD Nikon SP 2005
Cambo 23F 6x9, Olympus OM, Pentax M42, 6x6 & 6x7
De Oppresso Liber