Displaying custom data in a combobox

Hi everyone,

I need help in how to go about displaying custom data in a combobox. Basically what i'm doing is displaying the items of combobox as checkboxes. What I can't achieve is getting the combobox to display the checked items.

I think I need to do some work on ContentTemplate="{StaticResource SelectedItemsTemplate}" of the combobox but I really don't know how. I tried replacing it with my own datatemplate but how do i go on about getting the checked items inside the combobox? Please help.