Maybe you can fill up a recipe book? Imagine if Brewster expanded his business to be a lunchroom of sorts instead of just a coffee bar. And you earn rewards the more recipes you unlock or whatever.
Kind of like how you fill up the fish and bug encyclopedia I guess. This could actually sort of work right? Sounds fun to me at least.
Yes, that would be fun. I also thought of a diner of some sort, which could be combined with Brewster's caf? like you said. Maybe he can expand with also making other drinks than coffee, like fruit drinks and smoothies you can make with the fruits on the island. It would go great with the tropical island setting^^