sling. Learn how to use it. Its quick and does the job. Offhand...learn to grab what you can or just deal with it. I wouldn't carry anything just due to an offhand shot.
That said we often use a walking stick or cut one...
Prone, for longer shots, I"ve used my wife as a rest, a backpack, or just a sling.
You have used your wife for a backpack or a sling????
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