party favor vs keepsake

party favor and keepsake both are nouns.

Word	Noun	Adjective	Verb	Adverb
party favor	Yes	No	No	No
keepsake	Yes	No	No	No

As nouns, keepsake is a hypernym of party favor; that is, keepsake is a word with a broader meaning than party favor:

party favor: souvenir consisting of a small gift given to a guest at a party
keepsake: something of sentimental value

Other hypernyms of party favor include relic, souvenir, token.

party favor (noun)	keepsake (noun)
souvenir consisting of a small gift given to a guest at a party	something of sentimental value