Charlie not wanting two servings of energy drink (6)
I believe the answer is:
coffee
'drink' is the definition.
(I know that coffee is a type of drink)
'charlie not wanting two servings of energy' is the wordplay.
'charlie' becomes 'c' (phonetic alphabet: alpha, bravo, charlie etc.).
'not wanting' becomes 'off' (eg someone no longer eating something is 'off' it).
'two servings of' shows that letters should be duplicated.
'energy' becomes 'e' (physics symbol as in E=mc2).
'e' doubled is 'ee'.
'c'+'off'+'ee'='COFFEE'
(Other definitions for coffee that I've seen before include "Common drink" , "Common stimulant" , "Beverage from beans" , "Popular drink made from ground beans" , "Drink from 19s" .)