Do not spend on sakura's gift as a f2p, it's just a terrible idea because any whale can come in and take the number 1 spot after you're done spending. The number 1 prize also will only give 100 frags of a top tier ninja which is not enough to 4 star and bt them.

That said, for your curiosity;

5. "Sakura's Gift" -- July 1st - 23:59:59 July 7th:

- 20 Coupons/Ingots = 1 foodsack

- Rice Onigiri = 1 point, Salmon Onigiri = 3 points, Panda Onigiri = 5 points

- 1 foodsack = 3.15-3.6 points

1000/3.6 in bestcase = 278 * 20 = 5560 just to barely get on the rankings. Keep in mind that top whales will spend many more coupons than that, basically making your spending irrelevant.