One casually pegs out basic garments (6)
I believe the answer is:
undies
'one casually pegs out basic garments' is the definition.
I can't tell whether this defines the answer.
'one casually' is the wordplay.
'one' becomes 'un' (northern English dialect form of 'one').
'casually' becomes 'dies' (I can't explain this - if you can you should give a lot more credence to this answer).
'un'+'dies'='UNDIES'
Can you help me to learn more?
(Other definitions for undies that I've seen before include "Undergarments (colloq.)" , "Personal attire" , "Pants" , "Knickers (abbrev.)" , "clothing not normally seen" .)