Sign up for free online courses in whatever. (Shaw academy and Alison have some decent ones).
Read
Volunteer
Plan for your future
Plant some trees/plants/veg whatever
De-clutter your room
Write a novel
Decorate your room (paint/rearrange furniture/buy new furniture etc)
Do some DIY / wood work (start with something easy though if you're new to it)
Do a new hobby
Learn how to stargaze and stuff.
Watch netflix/putlocker
lift some weights
get a gf (she'll take up some time)
Build a computer
Sell stuff on ebay
Get a job.