You could make activated carbon by placing wood in a sealed
container with only a very tiny hole in it and heating it until the
wood is charred into activated carbon. Ideally, a tube leading
into the container would be used to force water onto the wood to
create steam inside the container though this is not essential.
(The main consideration is to not allow air to get to the charcoal
when it's being heated while having a large enough hole in the
heating container to keep it from exploding when the hot gases in
it expand.)