One on soft drinks during party gets the same again (5)
I believe the answer is:
ditto
'the same again' is the definition.
(I've seen this before)
'one on soft drinks during party' is the wordplay.
'one' becomes 'i' (Roman numeral).
'on soft drinks' becomes 'tt' (abbreviation for teetotal - not drinking alcohol).
'during' means one lot of letters goes inside another.
'party' becomes 'do' (do is a kind of party).
'i'+'tt'='itt'
'itt' inserted inside 'do' is 'DITTO'.
'gets' acts as a link.
(Other definitions for ditto that I've seen before include "Two dots say same again" , "couple of marks" , "Mark used to indicate the word above it should be repeated" , "Repeat the word(s) above" , "Dot it for the same again" .)