Zym Electrolye tablets
You can get the tabs in either tubes of ten or singly in sachets, which is handy if you're out on a ride and need to refill your bottle. The berry flavour is sugar free and pleasant: it's best made up an hour or so before the ride to let the residual fizz from the dissolving tablet disperse. Each tablet only contains four calories, so you'll need to pack food or gels to keep you going, but the mix of salts (Sodium, Potassium, Calcium and Magnesium) are just what you need to keep a balance in your body and fight dehydration and muscle fatigue.
Whether or not you believe the claims made for them, these Zym Electrolyte tablets are certainly convenient. You get 10 of them in a neat little green tube and all you have to do is pop one or two in a bottle of water and wait for the fizzing to stop.