MD80 CREW FORGOT TO EXTEND THE FLAPS PRIOR TO TKOF AT STL.

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DUE TO CONGESTION ON TAXI-OUT; SHUTTING DOWN AND RESTARTING ENG; AND PROBS (DISTRACTIONS) WITH PAX GETTING OUT OF SEATS; THE TAXI CHKLIST WAS COMPLETELY MISSED AND UPON APPLYING PWR FOR TKOF; THE WARNING HORN SOUNDED -- FLAPS/SLATS WERE NOT EXTENDED. I PULLED PWR OFF; EXTENDED FLAPS AND SLATS; CHKED WAS IN ORDER AND THEN TOOK OFF. THE AIRPLANE MUST HAVE GONE 800-1200 FT DOWN THE RWY BEFORE FULL PWR WAS SET. TKOF/CLB/DEP WERE ALL NORMAL -- UNEVENTFUL. IN REVIEW; 1) I NEED TO ESTABLISH A HABIT FOR FLAP/SLAT EXTENSION. 2) I NEED TO ESTABLISH A 'CHKPOINT' OR HABITUAL SPOT TO DO TAXI CHKLIST. 3) I NEED TO REALIZE NOT ALL COPLTS WILL BE HELPFUL IN JOGGING MY MEMORY; IF I FORGET TO CALL FOR CHKLIST. 4) I NEED TO DO AN 'INFORMAL' CHK OF THE KILLER ITEMS BEFORE CALLING FOR TAXI/TKOF LISTS. 5) I NEED TO NOT BE SUCKERED INTO ATC PRESSURE TO 'CLRED FOR IMMEDIATE TKOF.' I WOULD ALSO STOP IF THAT (GOD FORBID) WERE TO HAPPEN AGAIN TO AVOID EATING UP VALUABLE RWY. AFTERWARDS; I REALIZED THAT TKOF MIGHT NOT HAVE BEEN 'LEGAL' INASMUCH AS IT WAS NOT STARTED EXACTLY AT DEP END. IN FACT; VERY ILLEGAL. IT IS VERY SOBERING TO REALIZE THAT ONLY A SMALL WARNING HORN KEPT MY FLT FROM BEING A REPLAY OF THE ACR MD80 CRASH. THERE IS NO EXCUSE. WRITING THIS OUT IS HELPING TO CEMENT IN MY MIND THE SERIOUSNESS OF THIS AND WHAT I COMMIT TO DOING DIFFERENTLY IN THE FUTURE.