I make a point of keeping a few glass-encased votive candles in the house. You occasionally see them cheap in dollar stores. They burn for up to 6 days.
I have enough jar candles to last a year if using them at night for light. I took the number of hours they burn, figured how many hours I would need light at night for a year, and bought that many jar candles. I did that years ago and they are stored in boxes in a large storage area closet under the stairs in my house. That is backup plan B I probably won't need but they are there.