I own 6 thermacell units...and keep about 50 cartridges all the time.
You can buy 11 gas cartridges on **** that hold twice what a normal unit holds, and an adapter to make it fit your unit for about 10 bucks plus shipping, and all you have to get is bug strips then.
Stop at the duty free shop across the border and get a bottle of Amarula- its an liqueur made from an African fruit that elephants love to eat and when they ferment on the tree, the elephants stand under the tree, push it to shake the fruit out, and they proceed to get drunk on them.
I got a little tipsy one evening in camp myself and it made for some interesting conversation.