the most important thing in a first aid kit is the soft stuff between your ears. training, knowledge and the ability to rationally think through a problem are paramount. Providing assistance to the extent possible given materials, location and skill level and improve the situation without making anything worse is the goal. Imo, that warrants some discomfort on my part by carrying a full kit and not relying on others to carry something I or my party might need in the event it goes bad.
take the gear that you feel comfortable with. I've had two accidents so I consider the weight well worth it. My minimum kit in my helmet is a quick bleed kit in a zip lock bag: 4 nitrile gloves, 6 4x4's, a roll of kling gauze and a tiny roll of tape. imo duct tape is nearly worthless for wounds and makes more of a mess in first aid than it's worth. it leaves residue all over the area which attracts dirt and getting it off without reopening a wound is tough.
My main kit is 2.5 lbs and it goes with me on almost all trips. Improvisation is obviously important, but some things are easier to carry, imo. I don't personally believe in lightweight bper altoid type kits because the injuries one can get climbing are generally going to be more serious than a backpacker can get.
I personally think MEC's empty kits are the best value. I've never seen a pre made kit that was cheaper than assembling the contents at a pharmacy and buying an empty kit. Galls.com is a good source for bulk first aid materials.
