This has been done a million times before, but here are 5 things that I take on every photoshoot. It is really important to have a very methodical approach to photography equipment, even on the smallest of jobs.
Spare Cameras! I have 3 digital full frames. 2 35mm film cameras and 2 medium format cameras. There is often one being repaired at some point, but generally, there are three in my bag. Cameras break for a host of reasons from acts of god and carelessness to parts just wearing out. And trust me, they never break or fail when you are doing something unimportant. I have had cameras break on some really big commissions so I always travel with plenty. Assistants that I use often carry 1-2 of their own too. For really big jobs I have a few friends in the area that I give a heads up to “Make sure you have the following gear to hand” in case something really bad happens (kit bag being taken etc) so that my shoot goes to plan without any delays. Everyone stresses the importance of learning from your mistakes, but on this one, learn from others before you.
Second Card Reader. Card readers are temperamental, I have 2. I am currently using the Lexar ones, they are USB3 and do a good job.
Multiple Hard drives. As above, if I am in the studio then I have a set of studio drives + the one which then travels with me to my back up, off site. If I am on location then I take two travel drives with me, in case one fails. During longer shoots or when I am away I run a protocol of 3 external drives and keeping them all in separate bags and where possible in separate hotel rooms.
Gaffa tape. I have used this to attach cameras to places that stands wont reach, fix broken gear mid shoot and also to hold clothing in place. Make sure you have a roll of this with you on every photo shoot.
Back up details of everything on paper in case phone/laptop dies. This is something that stems back to a bad experience abroad. I was in a country where I couldn’t speak the language, my flights were delayed and I had no access to my phone (where all the key bits of info were stored). I was 22 at the time and it was far from pleasant. Luckily I managed to work it out in the end and find my way to the office. It does bring to light how reliant we are on technology though. A misplaced iPad or flat battery can really slow you down. So I always keep a copy of the key details and contact numbers on a piece of paper as a back up.