meal ticket vs coupon

meal ticket and coupon both are nouns.

Word	Noun	Adjective	Verb	Adverb
meal ticket	Yes	No	No	No
coupon	Yes	No	No	No

As nouns, coupon is a hypernym of meal ticket; that is, coupon is a word with a broader meaning than meal ticket:

meal ticket: coupon redeemable at a restaurant and entitling the holder to a meal
coupon: a negotiable certificate that can be detached and redeemed as needed

Other hypernyms of meal ticket include voucher.

meal ticket (noun)	coupon (noun)
coupon redeemable at a restaurant and entitling the holder to a meal	a test sample of some substance
a source of income or livelihood	a negotiable certificate that can be detached and redeemed as needed