Accidents, forgetfulness and natural disasters are inevitable. They’re almost guaranteed to happen. You could forget your memory card, it could fill up too quickly, it could get corrupted, you could run out of juice in your battery, forget to take it out of the charger, someone could bump into you and your camera busts into a wall and breaks the lens. It’s kind of like when you open your case to see all your strings broken or you don’t have any of your cables to plug in. Things happen and it sucks… a lot.
Obviously the best way to prevent any of these problems is to have at least two of everything. Yes, it could get a bit pricey but it could save you in the long run from losing a gig and potential other gigs via word of mouth. People are always talking.
If you forget batteries for the flash, most take AA so its fairly easy to get a hold of a new pack at any convenience store or maybe someone is nice enough around that has extra and will share (There are still nice people out there. While photographing a showcase, my flash batteries died towards the end of the night and another photographer there saw my troubles and gave me 4 brand new batteries!). Camera batteries will give you more trouble. You can find new one at most electronic stores but if you’re working the night shift, these may not be readily available. Try not to forget it! You could ask to reschedule but there’s a strong chance you will look unprofessional and could lose the job. It’s happened to me a couple of times, being forgetful can sure hurt you.
Things happen quickly and if you’re shooting manually (adjusting all of your settings…manually) there is room for error you may not catch. Sometimes you ISO could be to low, or the shutter speed is to slow, or a slew of other things. These are where your digital art skills (or a friends) can come into play. you can play with the color adjustments and filters back to how you want them to look, if they’re blurry, you could be out of luck, but if its movement, you can play with the filters and contracts and could have a pretty fancy looking photo going on there.