Cross functional teams are dependent on the type of people you select and the goals you have in mind. Making sure your cross functional teams have the right people is important. It isn't cost effective or wise to add a lot of people from various departments that don't have a direct impact on your success. Whether you are processing a new product or service you will need a team that can help you get from point A to Z.
Consider the general needs of the team to create your new product or service. There may be a need for designers, engineers, marketing managers, purchasing representatives, etc... Your team should be based on creating a successful launch.
You may not need everyone right away. During the initial product development stages you may not need everyone right away. Instead you may want to include people that are more focused on the creation aspect in the initial stages, manufacturing in the second stages and sales in their final stages.
Furthermore, you should consider having a few key people such as project managers throughout all the stages that understand how the entire product will move throughout the process. Having such people ensure that information isn't lost in any of the transitional stages.