Party on dry fruit cake (5)
I believe the answer is:
donut
'cake' is the definition.
(donut is a kind of cake)
'party on dry fruit' is the wordplay.
'party' becomes 'do' (do can informally mean a party).
'on' says to put letters next to each other (in a down clue, letters appear on others).
'dry fruit' becomes 'nut' (I've seen this in another clue).
'do'+'nut'='DONUT'
(Other definitions for donut that I've seen before include "American treat?" , "American pastry" , "ring coming across the Atlantic" , "Fast food snack" , "cake, American-style" .)