In the cover letter to the proposal, offer additional services like event planning, invitation design and envelope addressing, decorations, customized guest goodie bags, and other services if you'd like to outsource them.

When discussing ideas off-the-cuff with the client, give a ballpark price or a price range. Never commit yourself to an exact price until you've had a chance to price the whole job and make sure of your costs. A rule of thumb is to multiply your cost by four to give a price estimate to a client. (Since food cost should run around 25–30 percent of your costs, multiplying this by four is a reasonable way to get to the total cost to around 100 percent, or a bit more to give you some padding.)

Make contacts and develop relationships with other vendors before you offer to sell additional services to clients. Identify dependable vendors you know you can work with. You will take care of coordinating all of the services they will provide at the event so that the client doesn't have to. You can charge a premium (10–20 percent) for outsourcing because you are providing an additional service for your client. Outsourcing also allows you the flexibility to work directly with other vendors to make sure you share the same vision for the event. For example, you can make the dishes complement the floral arrangements by using a coordinating flower to garnish each course.

A successful catering proposal will address all of the client's specific needs and think of creative ways to solve problems the client may not even be aware of. Selling additional services is one way to let the client know you are looking out for them and are committed to making their event run smoothly.