What message was Garvey trying to give Cole with the ingredients from the brown paper bag?

"Garvey was trying to prove a point. He laid out salt, flour, eggs, baking soda, a bottle of water, sugar, butter, and molasses. He had Cole taste them. They tasted bad individually, but yet together the ingredients baked a cake. He tried to make the point that they taste bad on their own but good together. He wants Cole to be a part of something instead of alone.

Alone, each of the ingredients from the cake did not taste good, but Cole had the choice to take all of the ingredients and make them into something good such as a cake. This relates to his life. His life was full of things that 'didn't taste good', but he had a choice to take those ingredients/life situations and make something good out of his life.

Yep.