A B757 GOT A TKOF WARNING HORN ON TKOF ROLL AT MCO BECAUSE THE CREW HAD NOT SET THE FLAPS TO TKOF POS.

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GOT TASK SATURATED ON TAXI OUT FOR TKOF. TRIED TO ADVANCE PWR FOR TKOF. FLAPS WERE AT ZERO NOT AT REQUIRED SETTING OF 5 DEGS. EVENT COULD HAVE BEEN CATASTROPHIC. HAD IT NOT BEEN FOR TKOF WARNING HORN INSTALLED IN ACFT; END RESULT WOULD HAVE BEEN DIFFERENT. ENTIRELY HUMAN FACTORS CAUSED THIS NEAR MISHAP. BARRIERS THAT ARE IN PLACE AT MY AIRLINE (CHKLISTS/FLOWS) WERE BLOWN THROUGH. CAPT WAS IN A HURRY BECAUSE WE WERE RUNNING LATE; THUS JEOPARDIZING MANY PAX CONNECTIONS. CHAIN OF EVENTS STARTED WHEN CAPT CALLED FOR NON NORMAL SEQUENCE ON ENG START. AT OUR AIRLINE; YOU EITHER START BOTH ENGS AT THE GATE; OR START 1 ENG AT THE GATE AND 1 ON TAXI OUT FOR FUEL CONSERVATION. THIS PARTICULAR CAPT; ON EVERY ENG START; INSISTED ON STARTING 1 ENG AFTER PUSHBACK. THEN HE WOULD START ROLLING FORWARD TELLING ME TO CALL GND CTL FOR TAXI CLRNC; AFTER WHICH TIME HE WOULD IMMEDIATELY ASK ME TO START THE OPPOSITE ENG. THIS BREAKS THE HABIT PATTERN AND PROC AT MY AIRLINE OF CALLING 'FLAPS 5 DEGS; TAXI' AFTER STARTING BOTH ENGS OR 1 ENG BASED ON CAPT'S DISCRETION AT THE GATE -- NOT WHILE ROLLING. OTHER HUMAN FACTORS AND CONSIDERATIONS: 1) ON TAXI OUT; ACTIVE RWY CHANGED FROM RWY 36R TO RWY 18L CAUSING A HEADS DOWN SCRAMBLE FOR WT AND BAL AND TKOF DATA. 2) COCKPIT WAS EXTREMELY LOUD ON THIS ACFT DUE TO AN AIR FLOW PROB. 3) SQUAWK WAS MISTAKENLY SET FROM PDC DEP TIME. THAT IS; 'XXXX' INSTEAD OF THE ACTUAL SQUAWK. THIS BECAME AN ISSUE ON THE GND IN ORLANDO; BECAUSE MCO IS ONE OF THE FEW ARPTS IN THE COUNTRY WITH ASDE-X INSTALLED. THEY QUERIED US AND WE CORRECTED THE SQUAWK ON TAXI OUT (ALSO HEADS DOWN). 4) WE FORGOT TO DO THE BEFORE TKOF (NOW KNOWN AS 'TAXI') CHKLIST.