A cleaning jag is also one of those necessary items that can be problematic. Use a patch that's too tight with it and the jag can get wedged in the bore while trying to pull it back out.
Use one that's too loose and the patch will fall off.
Then an item called a patch worm is needed to fish out the lost patch down inside the bore.
That's a ramrod accessory with 2 spiral wire hooks that are designed to grab on to the loose patch.
No doubt some folks prefer using a patch worm to swab their barrel with, but the wire hooks can bend or pull out on some of them.
Even a shotgun size looped patch holder won't hold a patch large enough to fit very tight in a larger bore and won't clean effectively.
I use an undersize .41 jag with thick home cut patches. But a .45 might work well in a .50 also. I fold the patches over 2/3/4 times so that they fit nice and tight in the bore. It can be unfolded and refolded to expose a clean side and swabbed with several times.
With an undersize jag, the whole works won't get stuck in the bore nearly as easily.
I would rather fish a lost patch out of the bore than have my jag and ramrod get stuck, especially with a flintlock.
That reminds me, a ball puller or CO2 powered ball expelling device will make it easier in case you dry ball. That happens when one forgets to put in the powder before ramming the ball. Notice that I said "when" and not "if".
Then the ball will need to be extracted if a little powder can't be coaxed into the vent hole to fire the ball out.
So far, a jag, a patch worm, ball puller and/or CO2 discharger for when there's a dry ball.
A vent pick is used to keep the vent clear.
And a fouling scraper is used to help clean powder fouling out of the breech plug. But since every gun has a powder chamber with a different shape and dimensions, choosing the right breech plug scraper requires becoming familar with the shape of the gun's powder chamber. Some are flat, some dished, some deep and narrow, so the fouling scrapers have different shapes. And there are wire brushes to clean fouling out of the breech too.
If possible, it's desirable for one's ramrod accessories to fit onto an extended length cleaning rod or range rod that has a handle of some sort. In case they don't some thread adaptors can help each of those accessories fit onto the rod.
There are handles that can be added to a ramrod, some just slip on and others are threaded and those also come in a variety of shapes.
I don't see a ball starter being mentioned. That's used to help start the patched ball into the bore at the muzzle.
Most places that sell black powder will have some of these black powder accessories for sale.
Others can be found online.
Don't forget to bring a small piece of carpeting to protect the rifle's butt plate while loading the rifle with it resting on the ground or even worse, on gravel or cement!
Good luck.