If I can chime in about marathons. I have heard advice about improving energy levels and such.
I recently completed a century on a road bicycle. It was super tough, but with training and nutrition and a few steps it really makes a difference.
Before any big exercise, the week before eat very well. Skip the stuff you know isn't good for you.
Morning of the event: load up on carbs. pasta, oatmeal, etc.
15 minutes of stretching the involved muscles.
Gatorade during the event. I used to avoid it because I thought the sugar was not healthy, but I swear by it now.
After the event:
(this is a new one for me and it helped tremendously) You may think you have drank enough water/gatorade during the event, but now is the time to drink tons of liquid. try a couple of bottles!
15 minutes of stretching.
Then extend your feet and legs on a wall and hold them their for about 10 minutes. You may even feel the blood draining down your legs.
Then, (and I really like this step) go into a dark quiet room and have a 30 minute nap (set a timer).
After this post-event stuff, you will have recovered nicely from the event and good to go for the rest of the day!