If you’d like to offer a product under your brand that you don’t make you have two options: 1) develop that product and enter the market with your own version, or 2) find an existing version you like, and enter into an agreement for that company to manufacture the product for you, under your brand.
Depending on the product, you will need various representations and warranties in your contract with the manufacturer. If it’s food, you’ll need them to ensure that the food is properly labeled. If it’s a food supplement, you’ll want the manufacturer to warrant that they comply with all the necessary FDA regulations regarding health supplements.
Importantly, for a firm that focuses on intellectual property, the contract will need to outline quality controls, and how they may use your trademark in printing labels, and if they may use it in any other way.