Hello,

I think that content of cart should be erased when user logout. A simple
solution is to create file "event.FrontEndUsers.OnLogout.php" with content:
if( !isset($gCms) ) exit;
$this->EraseCart();

and add/remove event handlers on install/uninstall:
method.install.php: $this->AddEventHandler('FrontEndUsers','OnLogout',false);
method.uninstall.php: $this->RemoveEventHandler('FrontEndUsers','OnLogout');