Piecing one together is the best option IMO.
^^^ This is good advice^^^
The commercial first aid kits are just a bunch of bandaids. If you buy one big enough that it actually has useful stuff in it, then it's too heavy.
One day I sat down and listed the first aid experiences that I have actually encountered during sixty years of backpacking, camping, fishing, climbing and hunting. I built a first aid kit based on that. Here's the list.
8 ea Bandaids 1" x 3" fabric - Minor Cuts
4 ea Bandaid 1 1/2" x 4" fabric - Abrasions and Cuts
1 pad Moleskin 3" x 4" - Blisters
4 ea Moleskin Donuts - Blisters
1 tube Neosporin Ointment - Triple Actibacteria Ointment
1 roll Gauze, sterile - Wound Treatment
2 ea Gauze Pad - Wound Treatment
2 paks Quick Clot - Stop Bleeding
1 ea Battle Dressing - Major Wound
1 tube Aquaphor Ointment - Burn Treatment
1 roll Ace Bandage - Sprains
1 roll Vet Wrap - Sprains & Wound Treatment
1 ea Needle - Splinters & Ticks
1 ea Tweezers - Splinters & Ticks
1 tube Chap Stick - Chapped Lips
4 pills Antacid Tablets, chewable - Indigestion
I put everything in a small stuff sack.
I use to carry a Sawyer Extractor to use for snake bite, when I lived in Arizona and hiked in the desert. But I don't carry one in the mountains.
I've never needed a tourniquet, so I don't carry one. I figure I could make one with my belt or a rope and a stick.
I also carry a big first aid kit in the truck/trailer. But I leave it there. I don't carry it in my backpack.