Nutrition in Endurance Sport
I researched nutrition in endurance sport.
It turned out that human body needs a little bit carbonhydrates to improve water absorption. A good ratio is 6-8 % per litre which means one 375 ml bilberry juice bottle mixed with 3 litres of water.
Because sweating alters the body salt balance, it's good to add 0,5-1,0 grams of table salt to every litre of the liquid.
In case of more energy is needed, eat bananas. One banana, one boost.
UPDATE 2021-07-22: Raisins are better. Bananas get mashed in a bag. 30 grams raisins, one boost.