Bag, vest, belt, or backpack

It really depends on what/where I'm shooting. I have a back pack that can carry/store most of my kit so it's to heavy to bring everywhere so it normally gets left behind with what ever gear I don't think I'll need at the most convenient location(like in the car).

If I'm going to walking around and shooting for a long time(like at an event or hiking for wildlife/landscapes) I'll use a single/dual sling and a belt system if I need to bring other things like lenses/TCs/filter packs/speedlites.

If it's something that doesn't require a lot of walking/time(like stopping by a vista point for a landscape or BIF). I'll just grab camera/lens and and hand carry(sling over my shoulder if a tripod/monopod will be used. Filter pack and TCs if needed will either just be hand carried or put on standard belt(the used for my pants).

Underwater I use a Pelican case which keeps the gear safe and dry while easy to wheel around.

I'd like to pick up a couple of sling bags, one small and a bigger one(like the Tamrac Evolution series) for those times I'll be out for long time and will likely want to take pictures but won't be that often. I think a vest might come in handy at times so I might pick one those up as well since they're cheap even though I haven't had a real need for one.

I use a F & S vest and belt system with Cotton Carrier holsters.

Shoulder bag and a vest. You can't "work" out of a backpack. You can "carry", but it's just not on for quick lens changes like with a shoulder bag.

I voted Belt.. I have a lowepro computrekker that I can carry ALL my gear in (And do on all day hikes), but my typical setup is using my Spider holster clipped to my belt/camelback or lowepro bag with my 1Dmk iv and either 100-400 or 16-35 attached (depending on what I'm shooting). The Spider holster is so comfortable, that I can do all day hikes like the Glacier Point to valley floor trail in Yosemite and never once have a negative thought about my camera.

Sling Strap with either a fanny pack carrying accessories (light setup), or backpack for the full kit. I voted backpack.

I work out of a Think Tank Speed Freak. It is built like a tank! Perfect size for a couple of lenses, a flash or two & sometimes the second body if I am not wearing the double strap. I like how I can slide it to my back/side/front & also how the shoulder strap helps distribute the weight of the hip pack.

for racing, i use a big roller to get me to the track, but then it stays in the car/trailer/media center.
then i load up my shoulder bag with a couple small lenses (which ones depends on what i'm going for that session) and a body
other body goes on the 400 and that goes over my shoulder with a monopod
once i get to a spot, i might or might not set the shoulder bag down. depends how long i'll be there. i also might or might now put a lens on that other body and keep it on me. all depends on the situation.

Shoulder bag for couple hour shoot, I like the quick top access an visual for everything. Hip belt for short field trip or sports where I don't expect to be setting a bag down. Backpack and trekking poles for long hike to site or wandering around a shooting area. I like the even carry and the balance offered by the poles. As I get older my balance is nothing like it used to be. Haven't used my vest in years.

I know it's not good, but i just load my pockets with what I think I will need, and occasionally throw a lens case on my belt loop...I use a two camera sling strap (black rapid DR1) so, I carry two bodies, with lenses mounted, and often a flash ontop JUST IN CASE... then I put a prime or 2 in my pockets, and maybe a 3rd zoom lens.

Working is a Loose Term ..
It is important to define what exactly the tasks are and under what conditions.
My bag system is preferred when working out of my SUV for a day
but not when skydiving into Lake Tahoe.
But since 78 % is from my SUV ..