If you hate yourself enough, you can go do the ARR relics. The grinds for those take up a large chunk of time(mostly the books since you have to kill 3 of 10 different enemies, do 3 dungeons, and 3 FATEs which can take a while to spawn even when doing other FATEs in the area). Then there is the light grinding step, which if you have the class at 80 doesn't take as long(averaged 3 minute runs of Stone Vigil, getting 48 light per run when it's not on bonus, 96 when it was - total needed is 2000).

There is also any of the other relics you could go for(HW isn't as bad, SB requires leveling up in Eureka which can be a pain but is easier with the challenge log, and ShB which we only have step one of so far).

Glamour is always an option, trying to find that perfect glamour for each type of event(player held event or actual event released by SE).

Leveling up your alt classes is another thing to do(best use for sidequests really). Helps you learn at least the basics of the other classes so you can know when something isn't right in a run(like an ice mage, or completely single target in massive pulls) and be able to give at least a little guidance.

Can always go find a static and do the savage/ultimates.

I'm sure there is lots more, but that's just what comes to mind.