http://www.myprotein.co.uk/products/electrolyte_powder
100g should last you ~125lires of drink, ish, it recomeds 800mg per hour of intensive excercise in the heat so less electrolyte and more maltodextrin in winter.
http://www.myprotein.co.uk/products/maltodextrin
Not entirely convinced by the maltodextrin, as fas as I can tell it's not quite as fast release as sugar so shouldn't lead to a spike, and isnt as vomit inducingly sweet as the same concentration os sugar. But it is cheeper than buying fresh orange juice for the camelpack.
[edit] the RDA of slat is 6g as TJ said, but thats a maximum for an average person, you only need about 2g IIRC, the rest is just pissed out. Unlike most RDA's which are the minimum as most people dont get enough, more than 6g if you dont need it can be dangerous.
Also 'Salt' is just sodium chloride, 'electrolyte' (lucosade sport, SIS, torque ete) is a mix of sodium, potasium, calcium and magnesium compounds to make sure you have the right ballance.