I take an extra, throw a saddle pannier over the saddle. Put the chain saw on one side, Extra gas, oil, tools on the opposite side and go enjoy the day.
I have enough trouble getting all my horses exercised to leave one home. So any excuse to take and extra horse I'm all over it.
It's also great training for the horse to deal with the noise of a chain saw, standing pateniently while I get off and work.
And no it's not much work to trail a horse to carry a pannier. Hauling the chain saw is great training on packing