Hydration made easy
Science in Sport - is really my first go to for sports nutrition - however it only ships certain places and not the US - hence the break down below.
US
There's a whole variety of electrolytes out there available on Amazon but http://www.ultimareplenisher.com/ is a cheap and easy one that does have a good low calorie eletrolyte mix. One water bottle, two scoops, 20 calories, job done.
In terms of purchasing any others - if you're watching the calories do keep an eye on the ingredients, for example, your average bottle of Cliff-Shot is 80 calories and normal Gatorade is 200 calories (that said their G series is more sophisticated and 0-50 calories a bottle). Ultima has a good comparison chart http://www.ultimareplenisher.com/comparesportsdrinks.php
An option is to add 2 scoops of d-ribose to that mix per 24 oz water/water bottle for for a bit of muscle energy - but the debate over d-ribose is for another post. In the mean time this is probably the best information I've found on the web http://www.wholefoodsmagazine.com/columns/vitamin-connection/ribose-health-and-performance.
I have never understood why you can't import SIS http://www.scienceinsport.com/ into the US but there we are (and I really have tried). If anyone manages to get one of the Canadian distributors to ship into the US please do let me know, and instructions on what to use are set out below.
Rest of the world - definitely Australia, Canada, UK and Benelux
For the really low tech option - squash ie Ribena, orange squash or anything else like that, reasonably dilute - will do the trick.
For the high tech option, I can't recommend Science in Sport enough. Buying in bulk it's relatively cheap and it is really the best in terms of quality and research out there and that's been true for over twenty years.
Go electrolyte from SIS is great if you want the 150 calorie option ,http://www.scienceinsport.com/public/shop_product.php?selprod=6 and if you want the 7 calorie option then it's SuperHydro you're after http://www.scienceinsport.com/public/shop_product.php?selprod=18 and you can always mix up both to get somewhere in the middle.
Go hasn't yet gone down the d-ribose route so it's always an option to add.
Brief introduction to D-Ribose
I'll post more on this another day - but these are the two key quotes from the Whole Foods article http://www.wholefoodsmagazine.com/columns/vitamin-connection/ribose-health-and-performance
Seifert: In the supplement business, D-Ribose is a sound choice. Ribose, a naturally occurring pentose (5 carbons) carbohydrate, is important in every cell. Ribose is a crucial building block in the energy molecule of ATP. Furthermore, Ribose plays a very important role in our RNA (the intracellular transfer agent of our genetic code), and is a key compound in other cellular processes. Sports-oriented studies—mainly acute, high-intensity sessions—have shown the cellular energy benefits of using Ribose around exercise sessions. Performance enhancement using Ribose has shown that dose and exercise state, not attaining anaerobic threshold, influence the optimal benefit of Ribose.
Passwater: Allow me to translate the biochemical term “pentose sugar” for the benefit of some of our newer readers. D-Ribose is a “good” sugar, not a “bad” sugar. D-Ribose is used in key body structures such as those you mentioned including ATP (the energy storage compound) and ribonucleic acid (RNA). It is not “burned” for energy (i.e., it is essentially non-caloric at 1.6 vs 4 calories), as do what we normally think of as “sugars” such as fructose (fruit sugar), glucose (blood sugar) or sucrose (table sugar). Pentose describes the family of simple sugars (saccharides) having five carbon atoms as the backbone of the molecules, and D-Ribose is a unique member within that family.
Ribose is the only sugar used by the body to regulate the metabolism of nucleotides. Ribose is not used to fuel energy recycling like the “bad” sugars. Instead, it drives the process of energy recovery by actually making energy compounds and keeping them in the cell. Only Ribose performs this very vital cellular function.