Sacks and carboard used for packaging are often treated with a fire retardent these days so you may find sacking burns better if you give it a rinse first. I've heard that elephant dung is highly prised as a smoker fuel in Africa but that's a bit hard to find here in the UK so I generally start with small ball of newspaper and once thats flaming nicely I stuff in a handful of semi dry lawn trimmings. If the moisture content is just right they will burn for hours and produce plenty of smoke. Joe Trattle Norfolk England