Answer for Nutrition for endurance training sessions

There are a couple things that will be helpful.  First, water with electrolytes in it.  So water with salt and potassium added. Then you can fuel with MCT oil (easiest for your body to break down into ketones).  Coconut oil is 60% MCT.  You can do something like this:

Athletes and Low Carb

Or if you want to take it to the next level, this product is actual Ketones so they will fuel you within 30 minutes or so.  Really great for athletes. This would give you the fastest energy as it is already ketones.
http://mariamindbodyhealth.experienceketo.com/