The best snacks for you are going to be ones that you enjoy, fit into your overall meal plan, and keep you feeling full.
A combination of fruit/vegetables + a protein or fat source is an example of a nutrient-dense, satisfying, low calorie option. Remember that snacking isn't inherently a bad thing, you just want to make sure that when you do so, you make nutritious choices that aren't tacking on a ton of unwanted calories.
Here is a list of convenient healthy snack ideas that fit this criteria:
Greek yogurt + berries
Gainful protein shake with a banana
Apples or bananas slices + peanut butter
Cucumber and carrot slices + hummus
Bell pepper strips + guacamole
Strawberries + 2 oz dark chocolate
Almonds + grapes
10 carrots + 2 tbsp ranch
1 banana + 1 handful mixed nuts
1 high quality protein bar (aim for at least 12 grams of protein per bar)
3 cups green salad with your choice of toppings
1 cup mango + 1 cheese stick
1/2 cup edamame + 1/2 cup pineapple