"Crew Prepare for takeoff" ??

[Anastasios]

At transavia.com I know that the captain doesn't give that command.
First there is the welcome speech.
Safety video.
Cabin check (make sure your seatback is upright..etc, etc) <-This can happen or immediately after the video or during taxi.
Lights off speech (For safety reasons cabin lights will be switched off,etc) <-this one is optional. Or they say it during cabin check or just
before take-off.
The purser gives the command: cabin crew, be seated for take-off.
And then the purser calls the cockpit to tell them cabin is ok for take-off and captain has to wait with take-off for 20 seconds so the purser
can fasten his/her seatbelt as well.

If it is a long taxi it is possible that this is all done and you still have to taxi 10 minutes till take-off. It can also happen you are already at the
runway.

Only commands the captain give are:
cabin crew, arm slide bars
prepare for landing
disarm slide bars
doors may be opened.
(Also others like during turbulence, take your seats, and emergency commands ofcourse).

Anastasios.