One taking free voyage has to pack (8)
I believe the answer is:
stowaway
'one taking free' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'voyage has to pack' is the wordplay.
'voyage has' becomes 'away' (I can't justify this - if you can you should give a lot more credence to this answer).
'to' means one lot of letters go next to another (I've seen this in other clues).
'pack' becomes 'stow' (stowing is a kind of packing).
'away' after 'stow' is 'STOWAWAY'.
Can you help me to learn more?
(Other definitions for stowaway that I've seen before include "Ship's non-fare-paying passenger" , "One in a hold" , "Non-fare paying traveller at sea" , "Free rider" , "Fare-dodger" .)