I have three, but only use two because it's just too many dishes to have out with bottles/sippies/lunchboxes for two kids.

I just reuse the same set throughout the day and store it in the fridge between pumping sessions so I could get by with one. But when I pump for the last time of the day, I don't wash it and I need to pump first thing in the morning, so it's good to have an extra set on hand.

I pump 4-5 times a day.

How many sets do you own, and how often do you pump?