Comedian with case of lemonade for picnic (6)
I believe the answer is:
doddle
'picnic' is the definition.
(I know that doddle is a type of picnic)
'comedian with case of lemonade' is the wordplay.
'comedian' becomes 'Dodd' (Ken Dodd).
'with' means one lot of letters go next to another.
'case of' says to hollow out the word (remove centre letters) (like emptying a case).
'lemonade' with its centre taken out is 'le'.
'dodd'+'le'='DODDLE'
'for' acts as a link.
(Other definitions for doddle that I've seen before include "Something easily done" , "Snip" , "pushover" , "Piece of cake" , "Easy crossword?" .)