Picky eater’s vehicle containing 50% eggs (5)
I believe the answer is:
vegan
'picky eater's' is the definition.
'vehicle containing 50 eggs' is the wordplay.
'vehicle' becomes 'van' (van is a kind of vehicle).
'containing' means one lot of letters goes inside another.
'50' suggests halving the letters.
'eggs' halved is 'eg'.
'van' placed around 'eg' is 'VEGAN'.
(Other definitions for vegan that I've seen before include "One shunning animal products" , "Avoiding animal products" , "One not eating or using animal products" , "one not using animals" , "An extreme vegetarian" .)