About the only time I ever stretch is on a tour when I'm trying to recover from a 'hard' day so I can back up for the next. On most rides I warm up by spinning easy in the early part of it and building up the intensity as my legs tell me they're ready. I have the same routine for my commute (13km one way) as I do for rides exceeding 200km (except that I usually find somewhere to stop and eat something after just over 100km if I can).

P.S. I drink 5-10 litres of water/day on average. Riding or not.