List Oracle multiple rows into one w/o a primary key field.

I want to write the output of the below sql in a variable (varchar2 2000) inside a Oracle procedure. This could return multiple rows. How could I concatenate this into one -- so that I could always assign the o/p to the variable.
I do not see any primary key to LISTAGG on...

SELECT 'username: ' || s.username ||
        ', osuser: ' || s.osuser ||
        ', machine: ' || s.osuser ||
        ', sid: ' || s.sid ||
        ', serial#-program-terminal-sessinfo: ' || s.serial#||' '||s.program||'@'||s.terminal ||
        ', blocking_session: ' || s.blocking_session ||
        ', seconds_in_wait: ' || s.seconds_in_wait ||
        ', sql_text: ' || l.sql_text 
        FROM v$session s, v$sql l 
        WHERE s.sql_id = l.sql_id(+)
        AND ((lower(l.sql_text) LIKE '%mytab1%') OR  (lower(l.sql_text) LIKE '%mytab2%'));