Back at work next month. How big a stash of expressed milk did you really need?

Everything I read says start building a freezer stash early. I've been expressing once a day for two weeks, I have a small shelf of bags, and I'm already anxious it isn't enough. He's 3 months. A caregiver will be with him on my office days. How much did you have before going back, and how much did you end up using? I suspect the answer is 'less than you think', but I'd like to hear it from people who've done it.