Pretty minimal really, mostly what I’m capable of using with my (lamentable) knowledge*. Antiseptic wipe, a variety of plasters, compeed, safety pins, elasticated bandage, paracetamol, ibufren. Paper, pencil. Obviously if you are diabetic, suffer from anaphylactic shock, etc. then you’ll be taking the necessary kit to deal with that.
That will deal with most cuts and scrapes. Once you get to breaks and dislocations then it’s a whole different level. Mostly it’s stabilisation rather than treatment. Upper body injuries a generally walking wounded – I’ve self rescued with a broken wrist and dislocated elbow for example, Legs and pelvis are most likely going to be 999 and mountain rescue. @tjagain will be along shortly no doubt, best practice for paramedics has changed quite a bit over the last few years. (Edit: too late!)
There’s a section on first aid in this useful on-line pamphlet – https://readymag.com/u16005985/1375842/21/?fbclid=IwAR2HZGX5i0wpgzAsfjMbn0hQUMWY6PeLDgC0K7G62-dClO5tsxsUUvd1iWw
2nd Edit: from the above link – worth noting that Josh Kato is an ITU nurse, his kit is minimal so he’s relying on his knowledge and improvising.
*Go on a first aid course, ideally one with a slant towards outdoor sports.