Candles - stockpile on those candles! The worst time to realize you are out of candles is during a power outage! So, don't think you have enough, get up and take an inventory and put them in a spot that is easy to get to. The last thing you want to do is fumble around in the dark trying to remember where you put your emergency supplies. Candles are a good supplemental light. They are widely available and you can get them at a decent price. Remember, when purchasing candles to see at night, the wider the diameter of the candle, the more light the candle will give off. Tealights or votives will give you a little bit of light. Three pillar candles that are 3" in diameter will give you enough light to brighten a room pretty well. The bigger diameter, the more light the candle will give off.
Lanterns - another easy to get item, the cost is a little more. Coleman lanterns are a terrific way to have alternative lighting during a power outage. They give off good light and are easy to use. Make sure if your lantern uses a flint that you have extra's on hand.
Light sticks - a little harder to obtain, but always good to have on hand, and great for power outages. Unlike candles or lanterns, they are easy to light, most all you have to do is bang them on your hand and they light up. Cost can range from $10 - $100.
Flashlight - A good ole' fashioned flashlight is a must for your emergency supplies. This tends to be one of those items you know you have, but aren't sure where it's at, and when was the last time the batteries were replaced? If it was last year make sure the current batteries didn't leak and check to make sure they are still in working order. While your at it, stock up on extra batteries.
Crank lanterns - This is a lantern that can take batteries, or it has an internal battery that works by using a handcrank on the bottom of it. With this option, you don't have to double check on your battery stock, you will never be in the dark with this this handy lantern! Prices can start at $30.00
Spring is a good time to review your emergency lighting situation. The two easiest things to have readily on hand are light sticks and a crank lantern. Both products don't require accessories such as batteries.