Adding anything from a package to nice, fresh juice seems odd. I have found three things that I occasionally use to give juice an extra kick or just to have something a little different.
Chia Seeds: Vegan and gluten free, they add fiber, omega fatty acids, antioxidants, protein, and other vitamins and minerals. They may also help in weight loss.
Wheat Grass: alkaline, minerals, vitamins, antioxidants, protein, gluten free and vegan.
Pure Green Protein: Packed with protein “with the amino acid ratio of human muscle.” Great for mornings that I feel bad about not having a protein for breakfast or for using the mixed berry flavor to mask an unfortunate juice mix.
Do you have any favorites?
Real Woman's Health 
I always have fresh fruit with muesli and yogurt
I have just recently found a great, gluten free Musli. It has dried fruit in it and I use coconut milk with it. It is a new love, so please forgive my gushing. I also keep a bag at work for snacking.
Hmmm…I hadn’t thought about it recently…but I will now! Thanks!
i just got a juicer and haven’t made my first drink yet. when i make smoothies, i add spirulina (protein), matcha (vitamins, potassium, iron), or cacao powder (antioxidants). you can learn more about these and other superfoods, including the chia seeds mentioned here, at http://reasonedaction.wordpress.com/2012/05/18/supa-dupa-fly/. i’m going to check out the pure green protein – thank you!
thanks for the info. I just discovered cacao nibs and dried goji snacking.