Death chests are free for everyone. When you die, instead of keep inventory, the mechanic on Towny Kingdoms is to spawn a death chest with your items inside. A sign is also placed on the chest with whose it is, the date, and the time they died. They only last an hour and a half though, so be careful. If you want to see a list of your current death chests, you can run /cenlist, and if you're rank Knight+ you can use /cenfind <index> to find it. You can also use /ceninfo <index> to see how much time a death chest has left on it.
