Generally they give you a business which is experiencing some troubles in the different topic areas e.g. marketing or employment relations. Therefore you need to give suggestions on how to improve their marketing and employment relations. Such as new strategies or systems.
If you were to do a marketing plan don't do a very in depth one. That is don't cover all the elements. I personally don't think your going to need to include all elements of a marketing plan maybe focus on things such as situational analysis and marketing strategies??