Snake on top of tea packet? (4)
I believe the answer is:
boat
'packet?' is the definition.
(packet is a kind of boat)
'snake on top of tea' is the wordplay.
'snake' becomes 'boa' (boa is a kind of snake).
'on top of' indicates taking the first letters.
The initial letter of 'tea' is 't'.
'boa'+'t'='BOAT'
(Other definitions for boat that I've seen before include "See 12 Down" , "cat, for example" , "See 18" , "See 1" , "Water craft" .)