This can vary quite a bit from one gun to another for the same person that has several guns.
I personally like quick loaders,they are easy to carry, compact and fast, I thick the TC brand is best for me because I use them with PRB as well as sabot.
A compact kit for at least wiping out the barrel; including jag,patches cleaning fluid nipple pick[I use torch picks they have worked well on all nipples and breach plugs for me; if you don't have a removeable breach plug a CO2 set up for poping out a ball with wet powder or [this is not supposed to happened]without powderif you have a removeable breach plug the tools for removing it.
An extra set of quick loaders sealed in a ziplock bag,just in case[I like to have at least 6 shots I could take several deer and a bear here as well as any wild hogs I run across.
What ever capper works fast with that gun.
I always have an extra ramrod although I have never broke one I have had the brush hook them and had to go back looking for them, I keep the extra in the car in the gun case.
I also keep a tool kit with an addition of tools for guns in the car if scope or scope mount should be broke or loosen I take them off and have the iron sights "0" so I can use them. I had a scope go bad on a trip to Canada and the irons saved the day.
Hope this helps give you some ideas. Lee