Peg will add up to being on the wagon (8)
I believe the answer is:
teetotal
'on the wagon' is the definition.
(on the wagon can mean abstaining from alcohol)
'peg will add up to being' is the wordplay.
'peg' becomes 'tee' (tee is a kind of peg).
'will' is a charade indicator (letters next to each other) (I've seen this in other clues).
'add up' becomes 'tot ' (synonyms).
'to being' becomes 'al' (I am not sure about this - if you are sure you should believe this answer much more).
'tee'+'tot'+'al'='TEETOTAL'
Can you help me to learn more?
(Other definitions for teetotal that I've seen before include "Completely abstaining from alcoholic drink" , "Pledged to abstain from alcohol" , "Abstinent from alcohol" , "Abjuring alcohol" , "drunk? No way" .)