Battery power
I learned something interesting when my camera misbehaved back in December and I travelled to Death Valley with a rented camera body. The body came with one battery, and I grabbed the two that I had for my own (identical) camera as backups.
My camera batteries (yes, proprietary rechargeable batteries) were two years old. I hadn't noticed that the battery life was diminishing, but that fact jumped out at me as I used the newer battery that came with the rental body. I could still shoot with the older batteries for more than a day, not the couple of days I was seeing with the rental.
Before I headed out on this trip I bought two new camera batteries. At the end of the day today - my fifth day of camera play - I needed to charge one battery. That was the first charge of the trip!
Sometimes a simple thing like purchasing new batteries is a really good idea.