You know, a mid-size whiteboard can effectively replace most of (not all) your to-do apps and calendar on your phone. I'm just talking about planning for studying or something near that.
Here's mine: (sorry it's not in English but you'll get the idea)
As you can see in the picture, the right part is for the todos. The middle part is like day view of a calendar app. And the left part is for exams or reminders or anything that doesn't fit in the other parts