Sounds like something barman might ask regular? (5)
I believe the answer is:
usual
'regular?' is the definition.
('usual' can be similar in meaning to 'regular')
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for usual that I've seen before include "Normal, customary" , "Common or garden" , "Normally done" , "Customary - customary drink" , "Unexceptional" .)