This discussion may contain spoilers!
Here's what can be burned in Strongbadia the Free.
The game box in Strongbadia.
Strong Bad's bed in Bleak House.
The smole alarm in Bleak House.
Strong Sad's flag in Bleak House.
Strong Sad's constitution.
Strong Sad's bill of rights.
The orange and black Kimono in Pompomerania
The skull under the flag in Country.
The skull to the left of the bridge in Country.
The paper mache skulls next to The Turantula (Strong Mad.)
The misterious bush in The Homsar Reservation.
The candle holder to the right of the screen in The Castle.
Marzipan's U.N./Homestar's draft wheel thingie in Marzistar.