Tip: Include a little gift when you ship
Today it is not that expensive to have some pens or some flashy stickers made with your name or logo on it. Give your customers the extra smile, and send them a little more than they expect. It will keep them happy and make them return, and it does not cost you a lot.
I don't recommend lighters as promotional gifts, especially if you ship your goods international. Just too many things can happen, and if an empty lighter arrives it is not a good advertisement. Apart from that your package might be delayed if you send it internationally and some detector goes off on flammable substances.
Other than that, just choose something light and easy to ship. The possibilities are nearly endless if you have a look in a catalog for promotional gifts.