Long holidays means not much activities related to work. That means our productivity will be getting lower than our normal level. What happened next is we will not be able to recover as fast as we used to be when we started our job again in new year.
What i tried to do to keep my productivity is by giving some load even on my holidays. I managed to finish several material for next semester and also write several articles in my spare time. Of course it's not a full time task, but only in my spare time so that my body and mind is not so far away from my daily activities.
I also keep reading books while i'm at home. It keeps my memory of what i should teach next semester