(I'm so far behind I don't remember who started it - sorry? If it was you let me know so I can credit!)
Once upon a time, I boarded at a barn where the only thing you were allowed to have outside of your tack trunk was one pair of tall boots. That's it. My tack trunk is an old wooden chest that served as my great-great-uncle's tool chest, and as such it does not have modern conveniences like space for full grooming kits.
So my grooming kit was this small bucket that, if I tipped it sideways, would slide into the tack trunk. The problem with that was that you had to tip it just right, and even if you had the knack of it, half the time everything in it would fall out. I put up with it for years, because lo, I am lazy as shit.
Then, a friend who was riding Tristan on and off for me bought me a proper grooming kit, because by that time I was boarding at a different barn that did not care if my grooming kit was outside my tack trunk, and she took pity on me, and I think she hated the part where all the grooming tools fell out half the time. The story of my riding life is basically set to "I Get By With a Little Help From My Friends," like the time Hannah cut Tristan's boot velcro straps that had been too long for like 5 years.
For a few years now I have had a proper grooming tote, and what do you know? Having organizational cubbies actually means I keep this thing pretty darn organized.
Left to right: hoof pick, curry comb (pro tip: buy a child's size if you have tiny hands like me, it's much easier to manage), shedding blade (this lives in year round; when he's not shedding, he's muddy, and fuck if I can remember to cycle it in and out), stiff brush, soft brush, mane & tail brush, soft face brush.
These are the standards; right now, I'm stuck with the shitty Vetrolin liniment because I could not find Sore No More for a while. I got the EquiFuse in my Blogger Gift Exchange package last year and when I remember to use it I love it. The detangler lives in the grooming box because I will frequently spray it on his tail even when I have no intention of combing it out; it helps keep things from getting too bad.
This time of year, I also do a quick spray of detangler on his shoulders every few days to help keep his blanket from rubbing.
I always keep some array of meds and/or treatment things in the grooming kit. Right now, it's this fabulous Vitamin E ointment because I was treating Tristan's fly sheet rub with it, and No Thrush, which is this nifty powdery thrush stuff I'm trying out and like quite a bit.
Not pictured: a small towel that I usually keep there just in case, and generic Tums. I'd run out last week. I use the Tums, I'll be honest, mostly as a placebo for myself. I will sometimes feed them to him before the ride if he hasn't had his grain, or if he's looking a little iffy I'll feed them after the ride. In theory, they form a buffer and help prevent ulcers, which totally works in some horses. In practice, when he's 100% fine but I can't make my anxious brain shut up, I feed them to him and it helps. He eats them like treats, and they have zero negative effect and some small positive, so.