Get this Optimum Nutrition Amino Energy + Electrolytes Sparkling Hydration Drink 12-Pack for $12.48 (Retail $24.99).
Each can has 100mg of caffeine from natural sources and 5g of essential amino acids to support muscle recovery. They have electrolytes which will support performance & endurance, and they have zero sugar with only 5 calories per serving.
Shipping is free on a $25 order or get free 2-day shipping on any size order with Amazon Prime.