Later model MacBook Air and Retina MacBook Pros offer a feature called Standby mode. Standby essentially takes the contents of your RAM and stores it on the hard drive after your MacBook has been sleeping for an hour. This saves plenty of battery life. Unfortunately, it significantly adds to the amount of time your MacBook takes to wake from sleep when already in Standby mode.
By default, Standby is set to one hour (3600 seconds) by Apple. But you can adjust the settings using the Terminal app to whatever you wish. I’ve set mine to two hours (7200 seconds), instead of one, using the following command in Terminal application:
sudo pmset -a standbydelay 7200
I caution you though, setting the amount (in seconds) too high can kill the battery savings that Standby was meant to give you. And in the end, it only saves you a few seconds when you wake your MacBook from sleep.