Sometimes it's the little things that make a big deal, for me, it's AA batteries. Lots and lots of AA batteries.
I use two Nikon SB-800 flashes when shooting (they take 5 batteries each), and when it's a fast moving event (like a wedding) changing batteries needs to go off without a hitch.
The trouble for me is organization and accessibility. I have tried zip lock bags, Tupperware, pouches, and.... well you get the picture.
And as soon as the flash seems to slow (even a little) I change batteries, so I don't want to throw them away as they still have lots of life left in them (for my girls CD players and other energy sucking devices), so my problem is compounded organizing my fully charged batteries and (keeping them separate from) from my "take homes".
Then the Personal Battery Caddy came to the rescue (cue dramatic music here). I have three of the 12 pAAck battery caddy's in my bag and they work like a charm, no fumbling in a bag for batteries, no cover coming off the Tupperware and AA batteries going everywhere. No wondering which batteries are good.
These battery caddy's keep me organized, they're compact, and get two thumbs way up for their ease of accessibility. Convenience is another word that comes to mind.
And as I change batteries I put the used ones back into the battery caddy upside down so I can tell at a glance which is new battery and which is a take home.
Personal Battery Caddy is available for different battery sizes and mixed configurations, they are rugged, well made, and very inexpensive($6.95). There is even a 10% discount if you order three or more, and free shipping for orders over $50.
If you use batteries in your photography, you need to give these bad boys serious consideration!