Dropping all user tables/sequences in Oracle

If you’re not intending on keeping the stored procedure, I’d use an anonymous PLSQL block:

BEGIN

  --Bye Sequences!
  FOR i IN (SELECT us.sequence_name
              FROM USER_SEQUENCES us) LOOP
    EXECUTE IMMEDIATE 'drop sequence '|| i.sequence_name ||'';
  END LOOP;

  --Bye Tables!
  FOR i IN (SELECT ut.table_name
              FROM USER_TABLES ut) LOOP
    EXECUTE IMMEDIATE 'drop table '|| i.table_name ||' CASCADE CONSTRAINTS ';
  END LOOP;

END;