//Guardar elemento en Session
$session = Session::instance();
$rs_val = "juliopari.com";
$session->set('rs_val', $rs_val);
$ls_codex[] = array();
$ls_codex[0] = 0;
$ls_codex[1] = $O1;
$ls_codex[2] = $O2;
$ls_codex[3] = $O3;
$session->set('ls_codex', $ls_codex);
//Recuperar elemento de la Session
$session = Session::instance();
$rs_val = $session->get('rs_val');
$ls_code = $session->get('ls_code');
//Borrar elemento de la Session
$session = Session::instance();
$session->delete('ls_code');
$session->delete('rs_val');
//Saber si existe un objeto en session
$session = Session::instance();
$cart = $session->get('cart');
if($cart==NULL){
//crear session
}
Fuente: http://kohanaframework.org/3.2/guide/kohana/sessions