I always found that a day spent doing the following was time well-spent. And if you don't much like the idea of spending time in the holiday doing them (if you don't have a technical support team), another option is to take the computers out of use for the last day or two of term. I always found that as long as you gave people a lot of notice, and made sure there were alternatives they could use if necessary, nobody minded too much.
Anyway, here are the tasks (edit according to job function):
cross-posted at www.ictineducation.org
Terry Freedman is an independent educational ICT consultant with over 35 years of experience in education. He publishes the ICT in Education website and the newsletter “Digital Education."