My homebrew recipe:

1 Cup Sugar
4 Tsp Salt
2 Tsp Potassium Chloride (Salt Substitute)
2 Tsp Sodium Bicarbonate (Baking Soda)

Use 3 Tbsp per liter of water

For calcium and magnesium I just swallow capsules separately, although I know there are liquid forms available.

Mostly I just use HEED and Endurolytes - more expensive but simpler. On longer rides I can get calories from just about anything except fruit. On longer runs I use Hammer Gel and Endurolytes. I tried a lot of natural substitutes for gels (molasses, barley malt syrup, rice syrup, combinations of those), but they were all too high in fructose for my digestive system.