Here is a shot of me. The bag I'm wearing is no longer in use. I wanted something with a little better support...

You can see some of my gear clipped to me:
3 tripple locking biners
Rope (no kidding)
30' throwline
14oz. throwbag
Plus there is the Fresh Water Supply: 2liters (I used to use canteens on a belt with suspenders from an old BDU, now I use a bladder storage unit)
Then there is all the stuff in the bag that you cant see.
30' static kermantle line for double ended rig
several screw _link_s
Pair CMI ultracenders
2-24" loop runners
1-36" loop runner
Fig-8
Two cords for prussics (used to be for footloop, but switched to distel hitch)
Splittail
12oz. throwbag
150' throwline in folding bag
Gloves
Helmet (wearing that)
The question: do I need all that?
The answer: No, but when I do I want it in the tree with me, not on the ground or in the truck.
I clip the bag onto my Ness Saddle with a keychain 'biner, by girth hitching the carry handle with one of the 24" loop runners. It does weigh me down a little on the way up, but as long as I can carry that gear 2mi. in and 2mi. out I'm keeping it with me. If I know I'm going to have to go up SRT I will carry my Rack in too, but that thing is HEAVY, and I dont keep it handy (it is in the truck though)!
Hey! if anyone feels bad for me carrying that lump of throwline like that I'm accepting donations for bags to clip to my saddle

...whats another piece of gear when I've got all the rest of that stuff?
Climb Safe!
Icabod