One thing it has taken me a while to learn is the importance of taking in calories during a run - even a "short" run of 45 mins to an hour. During 100 milers, I am pretty careful to get between 200 - 250 calories per hour in, but on shorter runs, I tend to be lazy about it and think, "It's just an hour, I'll eat after."
I don't normally eat before a regular weekday run. I get up, get dressed and get out of the door before my brain can object. But, I have started making it a point to do a gel (100 calories) before I head out the door - usually with a little caffeine in it and the difference is very easy to see. My daily runs are better when I fuel before and during if the run is over 30 minutes.
I have tried many gels over the years - it is just the most convenient way to get in concentrated calories and carbs when you are on the move. I have also done the "all real food" thing before and it works great as well, it is just a lot more work and preparation. The gel that I have settled on for the last few years, thanks to a recommendation by Fawn, is Huma - energy gels with chia seeds and all natural ingredients. Most of the other gels out there have ingredients I can not pronounce where as my favorite Huma - lemonade - is made with cane sugar, water, brown rice syrup, lemon juice, powdered chia seeds, sea salt and natural caffeine. (click the image to check out their website)