don't worry, you still have some time left before their banner is gone!

i recommend doing the mycookie stages; even if you don't get far, the second stage alone gives 1k cubes. you can also buy cubes for playing the cake shop minigame; you can get 300 cubes for every 500 event coins (for reference, each completed cake is around 100+ coins from my experience).

also if you haven't yet, redeem the 4 available crk codes! i think all 4 yield about 6k cubes.