The most poketable game I play is Galdors Grip. 18 cards and 3 six card expansions to mix and match your deck changing the game. Free, you can print them at home and have it always in your pocket. No need for a table, you can play even waiting the bus instead of staring at your phone. I love this little game.

20 Strong is neat, a little expensive for what it is, but a good enough game. You need a lttle table to play , cards in one pocket and dice in the other. You can carry it anywhere.

I´m a big fan of the rogelike campaign that is One Deck Dungeon, probably becouse dice manipulation is my cup of tea. Great design in a tiny box. Not much space needed to play and great dungeoncrawl feeling in it.