Card games are usually easy to learn and so much fun to play. Even young kids can play “War” (the deck is split is half and each player flips a card face up. Whomever has the higher card wins both cards.)
So grab a deck of cards and play “War”, “Spit”, “Egyptian Rat Screw”, “Solitaire”. I am including a link with a a list and an explanation of 75 2 player card games here.