One of the most important, but often overlooked items, are rechargeable batteries and chargers.  They are not all created equal.  In the following video, Matt Granger (That Nikon Guy) explains the difference between conventional and low-self discharge batteries.  Also the importance of having a good battery charger that will give you better performance and longer cycle life for your batteries.

products mentioned by Matt in the video:

Powerex AA 2700mAh batteries: http://amzn.to/1RTh8yA

Powerex AA 2400mAh low-self discharge batteries: http://amzn.to/20XO5Ad

Powerex MH-C801D battery charger: http://amzn.to/1RTgNfp