my 5 cents:
contingency should not cover before take-off discrepancies.
in my opinion the easier way is to calculate 2nd sector including all known fuel augmentations (e.g. extended use of APU, longer taxi, manouvering fuel etc...), then when you elaborate the "min fuel at destination" in 1st sector flight plan, you're safe with legal requirements for the next departure.
That's on the paper of course, should sector one burn more than planned and make a dent on 2nd sector fuel, well that brown stuff happens
