Here's what I recommended (and carry) for an individual first aid kit (IFAK):

Core trauma kit:
2 North American Rescue CAT7 tourniquets (no substitution), prestaged for one-handed application
2-3 packs compressed gauze, ideally one or all treated with a hemostatic clotting agent
2 pairs of vented chest seals
1 6" pressure bandage, "Israeli" style or similar
Trauma shears
2 pairs nitrile gloves
Mylar emergency blanket
Sharpie for writing TQ application time

Not core trauma but good to have:
2 Narcan doses
Fold-up plastic CPR mask
Dispersible (powdered) aspirin for heart attacks
Runner's sugar gel, for diabetic collapse
Triangular bandage, sterile if you can so it can double as an improvised pressure bandage
Ocular baggage
2 chemical hand warner pairs for helping with core temperature in cold weather

If you have the space and it won't limit where you carry the bag, a booboo kit:
4 Saline wipes for wound cleaning
Pack of large steri-strips for wound closure
4x4 Non-adherent bandage
2 Burn gel packets
4 Normal bandaids
2 Antacid pills
2 3" Pieces of kinesio tape for blisters (round the corners; stays on better)

For protests, add 1-2 sealed bottles of water with sports cap for eyewash (use only clean water or saline, never anything else)

Normal rules are that your IFAK is only for use on you, but that assumes a) active combat, and b) everyone carrying one in the same place so others can kind it and c) everyone being trained to use it; do what makes sense in context.

Folks who have advanced training might want to add more stuff, but at that point you know what you like. Specifically, I do not recommend carrying decompression needles or nasal-pharyngial airways unless you've been trained on them — they're unlikely to do much good without training, and the needles especially can cause real harm if used incorrectly. Note: I am trained in first aid, but I'm not an EMT, etc. I have, however, spent a good chunk of time digging into stuff here and talked with friends with more training about it extensively. Happy to hear opinions from other folks with more training here too.

Finally, if you have the money, consider buying body armor, especially if you're doing ICE observer work. I recommend getting a wrap-around softt armor vest that's rated as class IIIA — one you can wear over an undershirt and under e.g. a hoodie. These provide a baseline of protection while being relatively easy to conceal, so you're not targeted specifically for wearing armor. While soft armor is less likely to stop rounds intended for you, it may keep you alive if you're hit by a ricochet or an untrained office shooting into a crowd or e.g. at someone on the other side of a thin wall.

Do get a vest that can also support hard plates for added protection when conditions warrant, and if possible also buy the plates. For plates, you want either the lighter class IIIA+ (not part of the NJI standard, but commonly used by manufacturers) or cjass IV, preferably the latter. Do not buy steel armor; it's very heavy and impact spalling from the back of the plate can cause almost as much damage as the round would have if the coating fails. Also, do not buy flat armor — it's very uncomfortable to wear; multi-curve is best if you can find it.
Your plates should be either UHMWPE or ceramic. For ceramic plates, make sure that your plates provide edge to edge coverage — there should only be a few millimeters of protective coating on the edge of the plate. Cheap plates may have a half inch or more on the edge of the plate where there isn't actually armor.

There are three plate shapes that you'll commonly see — SAPI, Shooter's Cut, and Swimmer's Cut. You probably want SAPI; the other two provide less coverage but more mobility for shouldering a rifle or swimming with armor on. You can also get side plates — standard front and back plates obviously only protect against threats you're facing. These add a lot of bulk, though and make armor very difficult to conceal; they're probably overkill.

You may wish to consider a helmet, but of course a helmet is likely to make you a target. You might be able to disguise a ballistic helmet as a bike helmet. The PASGT style is your best bet as a starting point for that sort of thing.