There are 7 crops needed: You will need to build farming plots for each and use the hoe to maintain them and water them. You need to have each one planted simultaneously on your island in individual plots.
Aloe - Tall. Green plant with red top - Found on islands - Cures Heat Stroke - Fairly common
Ajuga - Tall. Green plant with a purple top - Found on islands - Fairly common
Kura - Yellow Fruit - Grows in medium sized trees - Check starting island - Less common
Pipi - Yellow plant - Grows on ground - Found on all islands - Check starting island. Usually two per island
Potatoes - Grows in ground - Sometimes hard to see - Check starting island
Quwawa - Yellow-Green fruit - Grows on a small tree - Rarest plant in the game. Took me seven islands to find.
Wavulavula - Pink flower - grows on the ground - found on islands - fairly common