MLG FLC INSTRUCTED TO HOLD MOVES FORWARD TOWARD RWY. CTLR ISSUES NEW CLRNC.

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WE TAXIED TO RWY 19L AND STOPPED; #5 IN SEQUENCE FOR TKOF. ACFT WERE WAITING TO TAKE OFF DUE TO WINDSHEAR RPTS FROM ACFT (+/-40 KTS SPD CHANGE) AND TWR INST INDICATIONS. THE DELAY WAS MINIMAL AND WE MOVED UP TO #1 POS IN A NORMAL TIME (4-6 MINS). STERILE COCKPIT WAS OBSERVED; EVEN WITH PARKING BRAKE ON. WE DID A QUICK BRIEF OF WINDSHEAR PROCS. WHILE HOLDING #1; THE TWR STATED TO HOLD SHORT FOR LNDG TFC; AND I ACKNOWLEDGED (I WAS MONITORING FREQ AND DID NOT CALL HOLDING FOR TKOF). I TURNED ON AUTOTHROTTLE SWITCH OF B737-300 BUT I COULD NOT SEE THE AUTOTHROTTLE 'ON' LIGHT. I TOLD THE CAPT AND TRIED TO BLOCK THE SUN ON THE LIGHT; TESTED THE LIGHTS; AND MOVED THE AUTOTHROTTLE SWITCH A COUPLE TIMES. MY HEAD WAS IN THE COCKPIT. WHEN I LOOKED UP; THE ACFT WAS MOVING FORWARD. AT THAT MOMENT; THE TWR STATED (APPROX) 'I DID NOT CLR YOU ONTO THE RWY; BUT YOU ARE NOW CLRED FOR TKOF RWY HDG; TFC ON 2 1/2 MI FINAL.' WE TOOK OFF. THE CAPT WROTE HIS OWN FORM. I THINK BECAUSE I WAS DOING THE TKOF FLOW; WE WERE CLRED ONTO THE RWY. THE CAPT STATED NOT TO DO CHKLIST FLOWS UNTIL HE INITIATED THE CHKLIST TO PREVENT PROBS IN THE FUTURE. CAPTS INITIATE THE TKOF CHKLIST ON THE TXWY AND SOME NOT UNTIL AFTER CLRED. IF I WOULD NOT DO ANY FLOWS UNTIL ORDERED; IT WOULD NOT CAUSE CONFUSION IN THE CAPT'S MIND. OUR 8 ACFT HAVE DIFFERENT COCKPIT CONFIGNS. TO KEEP AHEAD; I DID A FEW FLOW ITEMS EARLY TO FAMILIARIZE MYSELF WITH SWITCH POS. IF ALL COCKPITS WERE STANDARDIZED; I MAY NOT HAVE INITIATED THE CHKLIST FLOW AS EARLY.