Look, food is likely a big element of holiday expenditure (7)
I believe the answer is:
airfare
'likely a big element of holiday expenditure' is the definition.
I know nothing about this answer so I cannot tell whether this works.
'look food' is the wordplay.
'look' becomes 'air' (something might have a certain air or look).
'food' becomes 'fare' (fare is a kind of food).
'air'+'fare'='AIRFARE'
'is' acts as a link.
Can you help me to learn more?
(Other definitions for airfare that I've seen before include "Cost of a flight" , "Money for a flight" , "One won't catch a plane without it" , "Price of a flight" , "flight damage" .)