>>909772New EMT here. Trained, but with little experience outside of carting old people off to die and patching myself up from a life of /out/, /diy/, /asp/, and /k/ related pursuits.
I personally like to have trauma shears because they're good for cutting off tape without digging into your skin, can quickly expose an injured area for assessment and treatment, and can cut through pennies when you're more bored than you are worried about dulling your $6 shears.
For gauze, I keep 4x4 pads and a couple of rolls. I think I ended up with some 2x2 pads, too, which (if you have room for them) are nice for small stuff and not having to dick around with cutting up a 4x4 pad. Rolls are nice because you can use them as padding, to stuff wounds, to wrap large patches of fucked up/torn off skin, etc.
Liquid bandaid is magic. Antibiotics, antiseptics, aspirin, ibuprofen: magic.
I keep athletic tape and self adhesive bandage wraps, and I just bought one of those rolls of water proof tape to play around with.
Butterfly bandages are super rad, I've used them on myself more than I would like to have. For anons who don't have room, /diy/ butterflies can be made with tape, though the real thing is much more convenient.
If it's a FAK I plan to use on someone else, I'll bring a stethoscope and a BP cuff because it makes the normies think I know what I'm doing. It also tells me a bit more about what's going on and gives me sets of vitals to pass on to a medic or nurse if things are really that fucked. I've never used them in an off the job first aid context when it mattered.
In winter, I keep dark chocolate (sugar and caffeine help keep hypothermia at bay), caffeine pills, more chocolate, chemical hand/toe/body warmers (usually x2 each stay in my FAK and I'll carry more if I actually intend to use them), and make sure I have materials for a Palmer furnace (pic related, I'll have multiple lighters outside my FAK but keep one set aside with a big trash bag and 2 or 3 tea candles).