I usually just take what's necessary, which may seem like a lot to some. Here's a short gear list of my camera gear alone:
Body
Canon 40D
Lenses
10-22mm
17-40mm
70-200mm
1.4x extender
Other
Velbon Carbon fiber tripod (usually remove the center column)
Filters (graduated neutral density, polarizer, etc..)
Remote Release
Memory Cards
Spare battery or two

Sometimes I may carry a backup camera body (digital or film). I normally hike around with my 1.4x + 70-200 on my camera for wildlife, just in case. If I'm out for just a day hike or trail run, sometimes I will take along a 400mm but I've never taken that behemoth backpacking.
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Greg
www.naturefocused.com