Folk regularly request small vessels for wine, say (6)
I believe the answer is:
flasks
'vessels for wine say' is the definition.
(wine might be stored in flasks)
'folk regularly request small' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'request' becomes 'ask' (to ask is to request something).
'small' becomes 's' (abbreviation - e.g. clothes size).
The alternate letters of 'folk' are 'fl'.
'fl'+'ask'+'s'='FLASKS'
(Other definitions for flasks that I've seen before include "Narrow-necked bottles, thermos or vacuum" , "Narrow-necked bottles, may be of vacuum type" , "Bottles with narrow necks" , "Glass containers" , "Containers for liquid, thermos say" .)