Dungeon Dice https://boardgamegeek.com/boardgame/136192/dungeon-dice
5-minute Dungeon https://www.boardgamegeek.com/boardgame/207830/5-minute-dung...
Pathfinder: The Card Game (although a bit long) https://boardgamegeek.com/boardgame/133038/pathfinder-advent...
Shadowscape https://www.boardgamegeek.com/boardgame/200359/shadowscape
Dungeon Twister https://boardgamegeek.com/boardgame/144525/dungeon-twister-c...
Welcome to the Dungeon/Dungeon of Mandom - https://boardgamegeek.com/boardgame/150312/welcome-dungeon
Love Letter - https://boardgamegeek.com/boardgame/129622/love-letter
Hanabi - https://boardgamegeek.com/boardgame/98778/hanabi
No Thanks - https://boardgamegeek.com/boardgame/12942/no-thanks
Archaeology - https://boardgamegeek.com/boardgame/191300/archaeology-new-e...
Linko/Abluxxen - https://boardgamegeek.com/boardgame/153065/linko
A great one IMO is "Hive". It is abstract, so no story or narrative, but it is easy to learn the moves, very portable, easy to play on any surface and can be very deep in its strategy.
There's a Duel version for random strangers on trains and such.
Tiny Epic * (there are several games in the series) might be good. Although it does not meet your time requirements, it has few pieces and is portable.
The random stranger part is tough though. Even simple games take minutes to explain (Hive is an example another user gave, which is a great portable game, but it would take about 5ish minutes to explain the rules). It is also likely that you'll win any competitive games against a new player.
Much as I want to promote board games, if you are looking for portable fast games, the app store is probably going to serve you better.