I think a lot of it is down to educating passengers to be more efficient.

How many times have we all been delayed by someone who puts his briefcase on his seat, opens it and blocks the aisle while rummaging around retrieving things he wants during the flight?

Wouldn't life be so much easier if everybody could get into the habit of transferring their books, sweets and water bottles into a smaller bag before boarding? That way it would just be a case of "get on - put carry-on in locker - sit down", and boarding would be so much quicker!