I use a Think Tank Speed Racer waist bag.
Pics here, with lenses and gripped camera:
http://www.cjcphoto.net/misc2/speedracer.html
The Speed Racer is the only Think Tank waist bag that is big enough to take a gripped DSLR. It will easily hold what you want.
When hiking to your photo destination, you can wear the bag in back where it is out of the way. When you get to a shooting location, you can simply rotate the bag around your waist to the front, where it is designed to work out of standing up or sitting.
This bag will get pretty heavy when loaded up to be used purely as a waist bag. I use a trick I learned from my old Tamrac 750 - I wear the shoulder strap cross-wise (from left shoulder to right waist). The strap takes some weight off the bag and keeps it from pulling down so much (also allows you not to have to tighten the belt so much that it is hard to rotate). It also allows you to simply unclip the belt loop and not have the bag fall to the ground. (It can be quicker to get into rather than rotating around if you have a jacket on.)
The belt itself uses Think Tank's modular design where you can fit optional accessories to it of your choice. In my case I put a water bottle holder on one side and a 'Chimp Cage' on the other. Normally I put a water bottle in that holder, but in a pinch I can put in a lens. The Chimp Cage normally holds 'stuff', but could hold a second, gripped body.
Rotated to the front, you can sit down without taking off the bag. And work out of it. Useful in helicopters and small planes where you have no space. Convenient on trains, buses, taxis, etc.
When traveling, I usually rotate the bag to the front, and wear a Think Tank backpack with more gear in addition. Problem there is you can't use the waist belt on the backpack, so all the weight ends up on your shoulders from the backpack. I only do this combo when traveling through airports as it gets pretty heavy.
The quality of the Think Tank bags is extremely good, as is the design for the most part. My only complaint is that the belt buckle design isn't a quick-change sort of thing, which would be really useful when switching in and out of a jacket. (Belt too tight with jacket on, or too loose with it off).