You can limit the available quantity on any item.  So, for example, if you have 30 tickets available for an event, you can create an event package for the ticket and set the item limit at 30 units.  When those 30 units are sold, the item will show as "sold out" and no additional items will be sold (unless you adjust the inventory up).

To do this, open the item in question.  

Click Restrictions on the left menu

In the field labeled "Total Available", enter the number of available units

Click "Save".

If you want to adjust the available quantity up or down, you can do so at any time by just modifying the number in the "Total Available" field.