Christmas activities for the last week of term?

I am a cover teacher in a secondary school, I'm about to complete my first term and I've settled in really well. For my last week before Christmas, I want some fun activities for my cover lessons but I don't know what we could do.

I cover years 7 to 11, all subjects, I find out who I'm covering first thing every morning so it's all a bit of a roulette. Any and all advice is very much appreciated!