meal ticket vs voucher

meal ticket and voucher both are nouns.

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

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

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

Other hypernyms of meal ticket include coupon.

meal ticket (noun)	voucher (noun)
coupon redeemable at a restaurant and entitling the holder to a meal	a negotiable certificate that can be detached and redeemed as needed
a source of income or livelihood	a document that serves as evidence of some expenditure
	someone who vouches for another or for the correctness of a statement