Contacting the local tour companies in your area is a great way to find tour specials for all your guests. Many tour companies offer backpacker specials and other promotions throughout the year. You can ask the companies for promotional materials that you can display inside your hostel, so that all your guests know what is available. This will help the local tour companies to grow, and that may make it where all your guests receive even better deals from them in the future.
If you notice that one or two of their tours are quite popular with your guests, you may want to consider adding it to your schedule of weekly events. That will encourage all your guests to do it together, which will allow them to all get to know each other better. The tour company may even give you and your guests a better rate for those tours.