I am trying to make a drop down list with information from the customer model … I was able to display either their first name or last name but not the full name since they are separate attributes
You should use the "active" versions of the functions. That is, activeDropDownList() which takes as parameters the model and the property which the dropdown will be created for. See the API for more information.
You can define getFullName() method in your model class which returns the concatenated names. Then, you should be able to use listData to fetch 'fullName' and generate the options for dropDownList.