Smoothies are quick and versatile! I also love multigrain toast with bananas and/or peanut butter. Another great option is eggs. Scrambled, boiled, in an omelette with cheese and veggies!
You can have a simple fruit like an apple, banana, or anything else you can bite on your way to work/school. You can also wake up like a few mins early and make a toast, put something healthy on it (peanut butter for eg.).
Hope it helps!