See that pack on the rider's back? The genuine article is known as a "Camelbak", but there are cheaper alternatives to this branded item. It's a little rucksac filled with water (or whatever!). A tube leads to the rider's mouth so he can drink on the move. VERY useful whilst off-roading in Thailand, but also very handy mid-France en-route to the Alps when temperatures can exceed 40 degrees Celcius sometimes!
If you don't get one of these before you leave (try Decathlon or outdoor type shop), you can buy them cheaply at the sports supermarket in Bourg St Maurice.