I'm not so much into low calorie snacks as I am fond of nutritionally dense, flavorful snacks:
roasted cauliflower is low cal and flavorful. Season as desired with whatever flavor profile you want.
roasted turkey breast on gluten-free crackers with a bit of mustard.
Dark chocolate chips. Really, you don't need much to get the full experience of intense chocolate flavor. And it's chock full of antioxidants! And a mood lifter! Yay chocolate!
For dessert you can start with plain greek yogurt and add vanilla, honey and fruit for a lovely, healthy treat.
Hard cheese is also a great thing to have for dessert. Just a little piece of cheese, with a small amount of nuts and a bit of honey is very very satisfying.