Is it legal to sell another company's products if the product is already available on the market?

I would like to start a cafe in the California area, but I want to use packaged mixes from a cafe in another state to prepare my coffee and pastries. Do I need a license or approval from the cafe to profit from its mixes?

You do not need a license to use the other company's mixes unless you intend to advertise your products using the other company’s name. For example, if you were to use Quaker Oats' oatmeal mix in your oatmeal raisin cookies and you wanted to tout the cookies as being extra special because you used the mix among the ingredients, then yes, you should obtain a license from Quaker Oats.

The reason is that you would be trading off the name and good will of Quaker Oats in trying to entice people to buy your product. However, if all you wanted to do was use the ingredient (without the advertising component), you could walk into your local supermarket, buy the stuff and use it.

However, if you contacted Quaker Oats directly to work out an arrangement, you might get a better wholesale price.