Most dark green, leafy vegetables have calcium in them. Eat your bok choi, broccoli, kale, collared greens . . . or you could try drinking soy milk. Nutella should not be your primary source of calcium.
For a light snack have three or four pieces of fruit. Apples, oranges, peaches, plums, grapes, bannanas etc. work well for me. Or bring a salad with some collared greens, carrots, celery, tomatoes, etc. just go very light on the dressing. You could also try eating some whole grain bread stuff (just be careful not to load on sugary/fattening toppings). What you don't want to have are the sugary carbs that you get in heavily processed foods (chocolate bars, granola bars, crackers, etc.) Those types of food are calorie dense without having much in the way of nutrients.