I use a combination of the above.
For carting my gear to my destination, I use the Canon backpack shown above. I bought it at Amazon.
My gear consists of Rebel XT, 50mm 1.8, 24-70 2.8L, 70-200 4IS L, 10-22, 430 EX II flash, cables, cards, etc. I leave the lens hoods home. If the tripod gets taken, it is put in a check through bag.
For going around the parks, I use the toploader on a belt. I decide ahead of time for the day which one other lens I want to use, and that gets put in a Lowepro lens case (it could go on the belt, but I just toss it into our park touring bag). I have to push my wife's wheelchair around in the park, and I found over the years that a shoulder bag (like my Crumpler 4 Mil home) swings around too much. I also found that keeping the camera around my neck tends to swing the camera around too much. The toploader on a belt works great. What I really like is that the zippers open to the outside, so the flap goes away from you. That make camera access greatly simplified. I just unzip, grab and shoot.
I can keep a card and a remote release and lightweight travel tripod in the TL pockets. If I let my shirt hang over the belt a bit, I don't even look so nerdy that my teenagers are any more embarrassed to be seen with me than normal.
Regards,
Boris