You absolutely want to be able to save your progress when you play Portal Knights, but a lot of people don't know exactly how to save the game. There is no save options, but instead you must rely on an autosave feature. This is generally saving very often, but not all the time, so you might want to force an autosave before you quit the game for the day.
To force an autosave in Portal Knights, simply travel to another island. Just go to the menu, find the island overview, and select any random island to travel to. While travelling, the game will always save, so you can now be sure that you keep all your stuff when you turn off the game.