Drink noisily, tossing off a litre — get up, then stagger (8)
I believe the answer is:
surprise
'stagger' is the definition.
(thesaurus)
'drink noisily tossing off a litre get up' is the wordplay.
'drink noisily' becomes 'slurp' (I've seen this before).
'tossing off' is a deletion indicator.
'a litre' becomes 'l' ('l' can be a synonym of 'litre').
'get up' becomes 'rise' ('rise' can be a synonym of 'get up').
'slurp' with 'l' removed is 'surp'.
'surp'+'rise'='SURPRISE'
'then' is the link.
(Other definitions for surprise that I've seen before include "Unexpected thing" , "One of spelt out words" , "is not what's expected" , "Something unexpected" , "Shock" .)