There's tons to do. ._.

1) Stock up on Grand Company Seals in preparation for being able to rank up.
2) Stock up on Ventures to level your retainers.
3) Get World of Darkness gear for other classes/retainers.
4) Do your daily roulettes for Sol and sell Sol items to make Gil.
5) Stock up on Atmas/Alexandrite if think you might want to make a relic for the new classe(s).
6) Do Ixali dailies if you can for crafter EXP and Oaknots.
7) Do Final Coil for your main's best in slot.
8) Stock up on cheap food for leveling.

This is what I've been doing since they announced the level 60 increase. I'm sitting on well over 1,000 ventures now.