Don't forget that, as the majority of aircraft were unpressurised, you'd be on oxygen & have your mask on at cruise altitude so no smoking. Even if you were flying a low level ground attack fighter like the original Typhoon you'd still be on oxygen even before starting as there was too many fumes into the cockpit from the engine. The exception might be the low level bomber runs like 617's Dambuster sorties or the USAF Ploesti raids but these would NOT be the norm.