These are very compact to carry and offer a nice quick boost and come in a variety of flavors.  I preferred the ones with little or no caffeen.

 

These taste like trying to suck down a tube of frosting.  The ones with caffeen made me feel a little crappy, but I am sure on mile 13+ I will be calling for it when my body says, "it's OK Justin lets just take a nap right here on the pavement".  The "roctaine" had waaayyyy to much caffeen!!  It felt like 5 cups of coffee.  Try these bad boys instead of coffee after lunch!  Can you say CRACK.

 

 

Gu Energy Gel Chocolate Outrage, 24 Pack (Chocolate, my favorite)

Gu Energy Gel Mixed Flavors 24 pckts (Mixed Case so you can test them all!)

Gu Energy Gel, Vanilla Bean, 24-Count (Most peoples favorite)

Gu Energy Gel, Roctane, Blueberry Pomegranate, 24-Count (2x Caffeen feels like speed)