there are lots of ways that I've seen an oildrum converted into a small charcoal kiln. The two that come to mind are simple with an angle grinder and no other tools
The first method (not tried it myself) is to cut a letterbox in the side and stuff your wood in there. Then you either set it alight and when good and hot you roll the drum over and cover any smoking gaps with soil to smother it. Or you treat it as a retort kiln, so fill and roll over into a shallow trench (so you can keep the drum airtight) and then light a bonfire around it, so cooking the wood inside the kiln.
The other method (that I have done) is to cut the top and bottom out (within the tim of the barrel), I cut the hole from the top to be about 3" smaller diameter than the bottom so I could use the piece removed from teh bottom as a lid. Dig a shallow and narrow (brick width/depth) trench in either an I, X or Y shape in the ground and set you drum ontop of it. Fill the drum with wood and place the lid. Then you have a mini kiln that has 2, 3, or 4 chinmnies to adjust the airflow. Using this method (with two air inlets) I normally get about 10kg of charcoal,which is about a wheel barrow full
Other than that, I would say BBQ or a smoker
