The major electrolyte minerals that need to be replaced are sodium, potassion, calicum, and magnesium. While sweat composition varies from person to person, an average liter of sweat will contain 20mg Calcium, 50mg Magnesium, 1150 mg Sodium, 230mg Potassium and 1480mg Chloride

A replacement drink also should have a small percentage of carbohydrate (ie. sugar). This actually enhances the uptake of the mineral.  A 2-4% sugar concentration is all you need. 

Here is a formula for a good replacement drink, with links to purchase the products. It will make about 150 servings. It has calcium, magnesium, potassium, zinc and maganese in beneficial amounts to replace electrolytes and to feed our enzymatic detoxification enzymes. 

1/4 teaspoon Source Naturals Mixed Ascorbate Vitamin C

http://www.vitacost.com/Source-Naturals-Ultimate-Ascorbate-C-Powder-8-oz

1/4 teapsoon Natural Calm Magnesium

http://www.vitacost.com/Peter-Gillham-Natural-Calm

1/2 teaspoon sugar or maple syrup

16 ounces of water

This blend provides 1000 mg of vitamin C, 30 mg of calcium, 60 mg magnesium, 85mg potassium, 3 mg zinc, 1 mg manganese and 2% carbohydrates.