I'm posting from mobile so please excuse the lack of links (I'll try to figure out how to post them anyway).

To keep themselves supplied with ammunition a musketeer carried a bandolier of wooden cartridges around his person, commonly referred to as the "twelve apostles". Inside the cartridge would be enough powder for one shot. This cartridge is upended into the barrel and would sometimes also contain the ball that would be shot.

If the apostle did not contain the ball, the musketeer might be carrying either a shot pouch which is just a bag full of lead shot or a wooden block that has both the ball and wadding pressed into it which he can place over the barrel and push into the weapon using his rammer.

Lastly, he would prime with weapon with a powder horn (ironically not generally horn at all) made out of metal or wood and covered in cloth. These may or may not have a measure on them that would produce a uniform sized priming charge each time. All of these items would be worn around the musketeer's torso.

For his slowmatch, he would have a very long length wrapped around his musket that would be inserted and removed from the serpent (the curved piece in the lock that pushes the match into the pan) and would probably carry a couple spares on him. This was not very cost efficient as the match would have to stay lit during the entire engagement whether the musket was fired or not, just in order for the musketeer's to be ready. The match would be lit beforehand by a unit leader, probably a sergeant, by a lantern that would have to be carried to each soldier individually.

The musketeer's would be protected by lines of more conventional soldiers, like pikemen, during their whole loading and firing procedures.

Note: unfortunately I cannot post any links but if you google "12 apostles bandolier" it will show what I'm describing. The fourth picture or so is a beautiful period sketch of a musketeer's equipment and shows the bandolier with a shot pouch and powder horn hanging off it. I hope all this helps!

I apologize in advance, I am at work on my phone.

I'll start with the fuse. Most black powder troops would have flint and steel in a haversack or a pouch. If their fuse DID go out they'd need to pull back a bit and relight it, and if it burned all the way through, which was unlikely, as most fuses were fairly long, and they were slow burning: most people would have kept spares with them.

They would keep them lit while reloading, but would pull the hammer back before pouring powder into the flash pan. This kept the fuse lit, and with less risk of a misfire.

Most soldiers would have their own supplies with them, such as pouches of bullets and horns fill of powder. It is not unheard of to have supply runners, but I believe it would be more likely for them to pull out if they ran out of munitions, or join other melee troops.

Most black powder troops were mixed with pikes or other melee troops, as they were fairly defenseless when they were loading. This led to the formation known as the Spanish Tercio, a Mix of pikemen, swordmen, and arquebusiers.

And if you're wondering, wet weather combat sucked if you had a matchlock or wheellock weapon.