Yes, I'm afraid you do need to hand over all work product that you created while employed. You were part of a team and if you try to subvert the team by withholding things that arise from your employment on the team you are trying to blackmail them into keeping you employed. I smell a lawsuit here.
But you should cooperate fully just as a way to boost your ...
Right now you are feeling "indispensable", although since you're leaving this position, you're apparently not that indispensable.
Hoarding knowledge to protect your position is an old technique, but as an academic, I would say that it's backwards thinking.
For one, your goal as an academic should be to grow all of humanity's knowledge. So as a matter of ...
In the end, you'll have to decide for yourself.
Properly handing over is decent, required by employment contract, and probably best for you (via professional reputation)
As you are already recognized for your helpfulness, don't sabotage that reputation.
Don't be surprised if your supervisor isn't interested in a proper handover, though.
Long version: Here'...