Q:

Unboxing ComboBox Items

since method Add() takes Object as an argument, can I add for example datatables, then unbox them? 
example:
cmbEmpresa. Items. Add(dt1);
cmbEmpresa. Items. Add(dt2);
cmbEmpresa. Items. Add(dt3);

then do something like:
datagrid.datasource=(DataTable)cmbEmpresa. SelectedItem;

EDIT:
and what about adding different type of objects, how can I unbox them according to the SelectItem's original type? 

A:

Boxing and unboxing actually means changing a value type into an object and vice-versa, so that's probably not the right term for what you mean. 
You can store any type of object you like in your ComboBox and cast back to the original type as needed.