I buy bulk frozen blueberries, frozen pineapples and bulk buy apples and bananas. I spend an hour or two cutting up the apples and bananas and then making individual portions/baggies of all four ingredients. If I ever see a banana going bad (or, per the toddler, “too many black spots”) I chop up and freeze banana for another time I portion fruit.

I buy spinach and kale every 7-10 days or so. I eyeball how much spinach and kale to use and mix them with the frozen bagged fruit portions for the daily smoothies.

(But based on pp’s comment, I need to add fat and protein!)

Always have on hand: kale, cucumbers, spinach, celery, green apples, ginger, carrot
Buy occasionally when I have a specific recipe in mind: pineapple, mango, beetroot, oranges, pomegranate, chard, various herbs

I drink green juice though, not smoothies. So freezing isn’t an option for me. I use the stuff on the top list almost daily so it doesn’t go bad (carrots less frequently, but they last longer). If anything is threatening to go bad I just juice it right away. Juice lasts three days in the fridge if stored correctly, and we have no trouble going through it.