Almost any nature provided fuel will work properly in the stove. Most fuels will provide about the same amount of heat, but different fuels have less energy (per unit volume), so will be consumed faster. If you are using a low density fuel, the stove can be recharged by simply adding fuel to the top of the stove while its burning.
Fuels must generally be dry in order to get the stove started. Wet or green fuels prevent the stove from reaching operating temperature. Once the stove has started, green or damp fuel may be added slowly.
Pellets are sold in hardware stores as fuel for traditional pellet stoves. Pellets are densified saw dust, and have very high heat content per volume. They burn longer than any other plant based fuel. The WoodGas camping stove will burn one load of pellets for up to 40 minutes on high power.
Chips made from chopping tree branches will burn very well in the WoodGas camping stove. A camp stove filled with wood chips will typically run for 20 minutes on high power.
Small branches can be chopped into sticks about 4 inches in length, and then stacked vertically in the stove. Total burn time for one load will be about 15 minutes on high power.
Pine Cones, Leaves, Grasses
These fuels are generally very light and will be consumed quickly in the stove. It is still possible to use them, but they must be added often to keep the stove burning for long periods.