There are lots of options here. Propane or white gas lanterns, rechargeable lanterns, chem-lights, battery-powered flashlights, oil lamps, candles, headlamps, small LED lights and so on. Keep a couple flashlights with extra batteries on hand. A headlamp is handy to keep your hands free while you work. A couple of oil lamps will keep darkness at bay at night. A few candles will supplement the oil lamps and you should be fine. Whatever methods you choose, make sure you keep fuel and batteries on hand and stored safely. Gas lanterns need mantles and spare parts. Generators will power lights and a lot of other appliances. They are great pieces of equipment to have. Good ones that produce enough useful power can be expensive. They will need to be run a couple times a year to check function and keep them in good shape. Stored fuel needs to be kept fresh and stable.