I posted a similar question recently. Though, my long days are 10-12 and I'm not on my feet all day... I have a commute that is about 8 miles each way, with a ~300 ft. climb that comes quickly after leaving work.

I have been eating a protein bar about an hour or so before I ride home, along with some water and coffee or tea. Just enough caffeine to get me home, but not so much to keep me up too late... A delicate balance... I also got a new light for my helmet which helps me see better on the ride home. I got the Exposure Diablo light (currently about $250) on Amazon and I am very happy with it. Very easy and quick to charge, light-weight & no bulky battery-pack.

Still, it is easier for me to bike home if my work day is 10 hours or less. When I work 12 hours or more, I just want to drive home.