You can refill your canteen (If it is low) and forage for meal (If you have no more rations) by clicking the river which you can see in the left side of the travel hub screen (Next to the large tree that Macsen is resting upon). The travel hub screen is the scene where you can choose to talk with one of your party members during the night, gives you the time to check your inventory, or just sleep if you don't feel like talking. (It always appear before a day ends).
Hope this helps!