Traveller put clothes in bag on back of truck that failed to start (8)
I believe the answer is:
rucksack
'bag on back of truck that failed to start' is the definition.
'rucksack' can be an answer for 'bag' (rucksack is a kind of bag). I'm not certain of the rest of the definition.
'traveller put clothes' is the wordplay.
'traveller put' becomes 'ruck' (I can't justify this - if you can you should believe this answer much more).
'clothes' becomes 'sack' (sack is a kind of clothes).
'ruck'+'sack'='RUCKSACK'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for rucksack that I've seen before include "A hiker's backpack carrier" , "large bag" , "Hiker's bag" , "shoulder-bag" , "traveller's bag" .)