Usually too humid,,, even when frigid cold,,, here to not wipe the pan clean after a shot. At the range I use an alcohol swab, in the field if I don't feel the need to be reloaded quickly I use the same, otherwise any bit of cloth, shirt tail, corner of sleeve, piece of rag tucked in my belt or tied to my shot pouch strap for the purpose.....
Having a bit of rag, even one of those small commercially available red "shop rags" handy is generally a good thing I find. Pan needs wiping, hands get dirty, knife blade needs wiping....
The only time I use a pan brush is when sweeping out dry unused priming powder when unloading if I didn't take a shot while out. I haven't found them sufficiently stiff and abrasive enough to do a good job cleaning burnt powder residue.
Fresh, commercially made, black powder (3f and coarser) doesn't absorb moisture from the air,,,, burnt powder residue does,,, a clean pan while in the field is a good thing.