How do you fuel your workouts?

I am planning on running a marathon next winter and have been reviewing my training schedule.  A 15K has been my longest race to date, therefore I haven't felt a need to alter my eating/hydration too much.  However,  I know this won't be realistic with a marathon.  And honestly, I think this is the first time I ever really reflected on the complexity of finding the balance with WLS, nutrition and endurance training.  

Does anyone have some recommendations on an approach to my diet as I increase mileage?   What does your day look like in the midst of training? 
Any particular issues/sensitivities you have faced in getting enough fuel throughout the day?
Any suggestions or personal favorites on carb sources during long runs? 

I would love to hear your thoughts and guidance. 

Thanks in advance! 

a lot of trial and error.  for me, i use poweraide zero and gels for my really long endurance training and events (anything beyond 2 hours).  it took me some time before i settled on what gel and what drink.  i've added endurolytes for my long bike rides in the summer, i haven't done that on any long runs yet (but most likely would if i were to run a marathon in the summertime).  i would seriously consider consulting a sports nutritionist (hopefully one with WLS experience) and i'm sure others can chime in with their strategies.  for me, a typical strategy for runs that last over 2 hours is to take in a gel every 45 minutes with plenty of fluid.  some people can only eat "real" food like bananas or sandwiches, some like gels, some like the chomps or sports beans, it really depends on your preference and what your stomach can take.  best of luck!