> You can take along a battery pack with usb-c and charge the macbook.

Actually not quite. The rules have tightened up significantly on powerbanks.[1]

First the same size rules apply as always, i.e. 100Wh, 100–160Wh with personal individual passenger permission and never above 160Wh.

Second, max two per passenger.

Third, you are prohibited from:

     - using them to charge devices on-board
     - recharging the power bank itself on-board.