This event, like most recent events, is very donut heavy. Over 900 donuts for the new premium items alone, never mind returning premiums that people might have missed in the past.
I like to keep 700 donuts in reserve (I don't know why I'm stopping at 700 rather than 500 or 1,000) and I buy mystery boxes with every six additional donuts I get to build up my multiplier with I&S boards & Ch6 vans. My bonus just went up to 800% with mystery boxes and I'm now waiting for the last few premium purchases for this event, plus the yellow submersible which I didn't get before.
My aim, for now, is to hit 1,000% multiplier and 1,000 donuts in reserve and then I'll see where the game takes me from there.