Exactly what's needed, and all that's needed, to get on board (4,3,6)
I believe the answer is:
just the ticket
'exactly what's needed' is the definition.
(I've seen this before)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for just the ticket that I've seen before include "Appropriate or desirable thing" , "Minimum requirement for one travelling" , "first class?" , "Perfect!" , "Exactly what's needed" .)