Something useful like gel (5)
I believe the answer is:
asset
'something useful' is the definition.
(I've seen this before)
'like gel' is the wordplay.
'like' becomes 'as'.
'gel' becomes 'set' (I've seen this in another clue).
'as'+'set'='ASSET'
(Other definitions for asset that I've seen before include "Useful or valuable quality or possession" , "Valuable item" , "Plus point" , "Useful item" , "Advantage, strength" .)