public class MainClass extends JavaPlugin implements Listener {
    private CombatActionBar cab;

    @Override
    public void onEnable() {
        cab = (CombatActionBar) getServer().getPluginManager().getPlugin("CombatActionBar");
        getServer().getPluginManager().registerEvents(this, this);
    }

    @EventHandler(priority=EventPriority.HIGHEST)
    public void on(PlayerQuitEvent event) {
        if (cab.isTagged(event.getPlayer())) {
            //TODO Remove items from player
        }
    }
}