welcome to DHC. The most important items are obviously pre-measured powder charges, additional caps and bullets, thrown in some snacks, a drink somewhere, knife and if using round balls some extra patches. I like a ball puller, bronze cleaning brush and cleaning cloths. I also carry a mult-function knife/pliers in case a ramrod gets stuck. 50-75 yds for me. Hope this helps some.
I like the higher cost clear plastic charge ones. Clear means I know they are loaded and ready to go. Make sure they have tight fitting caps. I usually put black tape over the caps to insure the caps stay closed in the field.