Keeping fit is always important. As mentioned when we first broke up, Joe Wicks has a good Youtube channel which has a daily exercise routine. Check that out here: https://www.youtube.com/channel/UCAxW1XT0iEJo0TYlRfn6rYQ. I'm sure Mr Cox would want you to be practising your planks. Also, if you have an interest in a team or individual sport, now is the perfect time to practise and improve. Whatever your sport or activity, think about all of the little skills that you need to play the game - practise makes perfect. For example, if I enjoyed playing football and wanted to improve, I would think of small skills I could improve. I would also spend a lot of time practising with my weaker foot to try and improve that. If you can't think of activities to do, I'm sure YouTube and the internet will offer you ideas.
There are some good challenges below. Perhaps start at the first level and see how far you can get.