After riding and Mt bikes for sometime now I have come to notice something strange to me.
How everyone carries stuff.Seems everyone caries pretty much everything in a Hydro pack, or not at all. I don't get why some of you don't use a small Seat Bag for some of the regular things. Bike tool, Tube, patch kit,Point and shoot camera, Cell Phone. It just make so much more sense than putting everything in a back pack for many reasons.
- 1. Weight is now lower
- 2. Less weight on Back
- 3. Easier access (don't have to fiddle with the pack to whip out the camera)
- 4. Tool's, tubes & Patches are always there ( ever want to go for the short "just do it" ride where you don't really need the hydro pack?)
If it's weight that some are worried about, well, YOUR STILL CARRYING IT! just you have now lowered you center of gravity. Hey it also helps as a fender so you don't get sprayed as much by mud...
( ok, not really much of a help but it sounds good) 
Now I'm not talking those big travel bags but a small or mid sized seat bag... If you think it's
"WIND RESISTANCE" well,
IT"S A MTN BIKE!! jeeesshhh

I just keep seeing these
HUGH packs people are sweating on their back and wonder why when a good portion could be lowered and not carried on your back which will make your ride that much more comfortable.

Anyway, just an observation.