Since saliva is one of the seven "liquids" (a subcategory of water, cf. Machshirin 6:5), would licking or sucking on one's own fingers fulfill the obligation of Mayim Acharonim?
Water that is fit for Mayim Achronim:
One shouldn’t use scalding hot water, rather lukewarm water is permitted and it preferable to use cold water. Hot water that cooled is also permitted.
Bitter, dirty, or smelly water not fit for animals to drink is permitted.
Saliva is unfit; if nothing is available is better than nothing. (Sources cited, there are: Peni Mabin O”C 38, Minchat Elazar 3:54, and Sherit Yehuda Blum 17 are stringent against the Torat Yekutiel Rosenberg O”C 6 who is lenient)
If there’s no water, one can use other liquids but not wine, yet if nothing else is available then one should wash with wine.