Do you have any of the following?: Hot water bottles? Medium to large glass jars with lids? Large Ziploc bags? Anything that you can put water into and seal it tight?
Besides the hand warmer packets, you can do the following: Since you have a wood cook stove, half of your battle is already won. In preparation, set aside large water jugs of fresh clean water. In some communities, when the power goes out, so does the water. Especially if you are on a private well. So, set aside a fair supply of water first of all. Some for the incubator, and don't forget for yourself as well.
If the power should go out, or you even think a power outage is imminent, start boiling water on the cook stove. When the power goes out, your water will hopefully be ready. Now it's only a matter of filling the hot water bottles, jars or even Ziploc bags. Before the temperatures in the incubator have a chance to drop significantly, you can put a jar or two of the hot water inside. Just be sure not to let them come into direct contact with the eggs.
Another thing to give some thought to is how to keep the temperature up in your incubator without resorting to changing out the jars of water every half hour. For this, gather up all of your thickest bath towels. You can fold your towels in half the long way and drape them over a clothes hanger and hang them near the wood cook stove. or simply drape them over the back of a kitchen chair.
This will keep them nice and warm. When the power goes out, and after you have put the hot water bottles/jars/Ziploc into the bator, then wrap the bator with the nice warm towels that you've kept near the cook stove. This will provide an additional heat source while preserving the temperature to a small degree inside the bator. Just be sure to keep the viewing panel clear so that you can easily monitor the temperature of your incubator.
You can also dry baking a dish of rice in the oven of your cook stove. Bring the temperature of a glass casserole type dish of rice up to about 300F. (NO WATER IN RICE!) Place the dish as far away from the eggs as possible. In the absence of a glass dish, a small aluminium dish will do as well. Glass just holds it's heat much longer than aluminium. But, with the dish of rice, you will need to monitor the temperature very closely. Depending on the size of your bator, and the size of the dish of rice, this might be too much, and you could run the risk of overheating the eggs.
Probably the easiest thing of all that you could do is to bring the bator into the kitchen and set it near the cook stove. Not to close of course. Don't want to cook the poor little darlings! Keep the doors to that room closed off and then crank up the fire in the cook stove. Even keeping the kitchen near 85-90 is going to make the job of keeping the incubator at the right temps just that much easier!
Keep us posted and update when the skies clear up. What day are you on in your incubation? Hopefully nowhere near the end. Best of luck to you. And try to stay warm!