Valuable sort perhaps Texan behind film (5)
I believe the answer is:
asset
'valuable sort' is the definition.
(I've seen this before)
'perhaps texan behind film' is the wordplay.
'perhaps texan behind' becomes 'ass' (US term for one's behind).
'film' becomes 'et' (E.T. the Extra-Terrestrial).
'ass'+'et'='ASSET'
(Other definitions for asset that I've seen before include "Beneficial thing" , "Item of value or advantage" , "Resource; advantage" , "Valuable thing" , "Something well worth having" .)