What what medicine should you keep in the first aid box?

This can depend on two things,

1)What your purpose of the first aid box is, for example: is it for personal use? Is it for a workplace?

2)Your level of training.

A basic first aider you are not trained in giving/prescribing any medication therefore you should not have any medication in your first aid box. However, an exception to this can be aspirine, as a basic first aider can give someone aspirine if they suspect they are having a heart attack.