Besides accommodation, you’re free to offer travelers whatever other benefits you’re able and willing to give them. The more rewards you offer, the more interested travelers will be in your position. You can offer them daily meals, such as breakfast, lunch and dinner and - or the possibility to use the kitchen to prepare their own meals.
Apart from food, you can also offer them free tours around the city, free classes (languages, Yoga, permaculture etc), free laundry, discounts on local restaurants or bars, and much more! You can take a look at all rewards you can offer travelers in your position’s page (Listing → Volunteer Positions → Edit → Rewards).
Remember, it’s always a good idea to share meals, classes, discounts, experiences and other rewards with travelers! Some, for example, might prefer positions that offer breakfast over the ones that don’t offer any meal.