Now days?

Extra layers.

As far as MZ stuff since going to tool less breach plugs I carry a Bore Snake to do a routine field cleaning along with a welders tip and drill bit to keep the breech plug clean, all three items weigh practically nothing and take up very little space in my pack.

Depending on where I am hunting and how long the walk in is or how long I plan to be out I also keep anywhere from 3 to 5 Speedloaders with extra primers in a capper.

Having broken a few slings in the past I always carry some rope to use as a back up sling,