Top Voted Answer
I missed this the first time too. Once you have the cakes you have to offer them to the following people.
Doc, Edna, Cueball, Trixie, Guy, (the one on the high school steps) Arthur Mcfly and young Emmet. For the last one you have to offer it to him while he's still working in the lab. Then you've got it. theone489 - 6 years ago
The cakes you're looking for are the algae cakes, which can be acquired from Cueball, who eventually shows up outside of the high school next to a truck. Natedogg316 - 5 years ago
This question has been successfully answered and closed.