On the interface of Summer Event, there's a *on "Ingredients" there .. Click that one and see where or how the ingredients can be obtained .. For the 2 that you mentioned, if i remembering it correctly, that's from doing 2 Wanted Missions and winning Arena 2 times ..

If you happen to lack 1 or more ingredients to prepare a set of food, you can ask your friends in-game to send you one if they have excess food ingredients since each player can only prepare 1 set per cycle ..