I'm all about having ALL THE THINGS ALL THE TIME when I go to class. There's a time to be minimalist, but at a multi-day class I've paid good money to attend, knowing I have everything I might need, including multiples of something this, is a small comfort that lets me stay in the game mentally on the class itself.

I have one of these:
https://www.homedepot.com/p/RIDGID-P...CTSS/315289493
that i fill out. I also have this extra crate that ties into it: https://www.homedepot.com/p/RIDGID-2...5905/206291778
Together these four modules are really verstile.

At an indoor class, it becomes a rolling workstation that allows me to stand while I load mags, etc.
At an outdoor class, i can stage it in the shade, in the "classroom area", or on a tailgate/back of SUV (unstacked) to give me a workstation (when I had a pickup with a locking hard cover - that was perfect and easily secured). Again regardless of tables or other facilities, it provides a standing platform to work from. Not spending my mag jamming sessions hunched over a range bag with all my belt gear jammed into my belly is a big win.

I load it out like this:
Big bottom box is least likely to use a lot - tools, armorers stuff. Spares of eyes and ears that i hope i don't need. Duct tape, zip ties, hammer, shop towels, etc.
The middle sized box is mostly guns - main and spare(s) in soft cases. Extra mags. Big box of extra ammo if round count supports it. Spare holsters/pouches. If I need to snag that box, lock it or leave it locked up elsewhere for security reason, it's easy to pull out of the stack.
The crate can either go on the very top, as a catchall, or can be 3rd in the stack. Great place to just toss stuff (hat, jacket, gloves, stapler, sunscreen, lunchbox). It's lightweight if you want to grab it and carry it down to the line with items if that's how the range setup dictates.

The top, flattest toolbox i like to have on top though. It helps to see how it is laid out: 2nd/4th pictures here: https://www.homedepot.com/p/RIDGID-2...1735/205440492
It's got 6 removable organizer cups and a flat open area. I stage loose ammo in the cups (which I can grab and carry if needed). The open flat area is workspace. I dump empty mags in there waiting to be loaded, and partials go into one of the cups, and loaded mags go into different cup or cups. Also keep lube and immediate need tools there in a cup - which also contains it if the lube spills or something. And when it's stacked up, that's all right about waist height to be a nice comfortable work station.

The wheels aren't good enough to drag it around at an outdoor match on gravel and rocks. But various boxes can be transposed into a wagon if that floats your boat.

And at a class i usually try to have a cooler separate - a big one if it' summer, smaller one if it's nicer weather.