I carry some of my owners manuals with me. Depending on the gear I’m carrying, the complexity, etc., I usually have a few with me. As much of a tech geek as I am, I’m still a little old school about some things. Speedlights, for example, have features I rarely use, and the menus can be difficult, and some of the symbols aren’t as descriptive as they could be, so the manual can be handy.
The good news is that almost all manuals are available online from the manufacturers’ websites as PDF files. What is also good is that all eReaders, including Amazon’s Kindle, Barnes & Noble’s Nook, the Kobo (they’re still around even though Borders isn’t), Sony’s eReader and others can display PDF files. What this means is that you can simply download the file to your computer, then transfer it to your eReader. Of course, if you have an iPad or other tablet (e.g. any flavor of Android tablet or a Blackberry Playbook), this will work just as well.
You can save valuable space and weight in your gear with an eReader or tablet, and if you find yourself with downtime waiting for the right light, you can have books, articles, games, etc. with you to keep yourself entertained and informed. 
You can also download some manuals just to look at their features if you’re thinking about buying one. Nikon’s website locks out printable versions of the manuals on some items without a serial number, but you can download a viewable version to view online and at least on the Mac, it can be downloaded by entering the URL in the downloads window.