Bananas with breakfast. Go down, digest, and if need be come up easy.
Every other bottle of water , use gatorade of something like that. Sweat and urine wash out the salts and other stuff. You need to replace.
If you are racing a six hour period, train for eight hours at a time.
Heart rate go up with excitement. Wasting energy and focus. Relax or meditate for the hour before start time.
At the race start go out at 80% effort. Way less chance to cramp at this pace. Longer it goes on the more 100%r's you will pass. 110%r's are increasing the chances of crash/mech/blowup, don't fall into that for an endurance race. At the half way point you'll get a measure of where you are in the race. Form there you can decide if this paced effort will get you to the finish or even finish first. Or if there is a chance for the all out effort to get a win will do. By not going all out to this point your tank should have the reserve to win the sprint.
good luck and post a RR.