I usually pick the same maps in casual mode, is there a way to save it so I don't have to select them every time I start Team Fortress 2?
This feature got added with the Scream Fortress 2016 Update, the update notes read:
Added "Load Saved Settings" and "Save Current Settings" buttons to the Casual mode Map Selection menu
The up-arrow loads your saved selection while the down-arrow saves it. If you are using a custom hud you might not see those buttons if the hud was not updated in quite some time.