Something worth having is found in cassettes (5)
I believe the answer is:
asset
'something worth having' is the definition.
(I've seen this before)
'found in cassettes' is the wordplay.
'found in' says the answer is hidden in the clue.
'ASSET' is hidden within 'cassettes'.
'is' acts as a link.
(Other definitions for asset that I've seen before include "blessing" , "Anything of value" , "Tessa (anag)" , "One bringing benefit" , "A thing of value" .)