Wheelchairs and luggage?

Seeing as I'm booked to fly out to Greece, spend a week sailing and then four days in Athens, and I'm travelling with the chair, I need to work out the logistics of luggage when wheeling. I'm aiming to travel fairly light, but bulk does add up regardless. I might just manage with the current bag for the chair-back, I'll have to do a trial load and see, but it will be tight and that doesn't have a lock on it, any thoughts from more experienced wheelies greatly appreciated.

Station 11, Emily St John Mandel

 If anyone has been meaning to read Emily St. John Mandel's A C Clarke Award winning 'Station 11', the Kindle edition is currently £1.79 on Amazon UK.