Well, i think minimally, you should have 2 to 3 days supply stored in your freezer. Dont think you need to store alot as everyday you will be bringing back milk for the next day's feed. Meaning, say you start work on Monday, your baby will be drinking the frozen stores during the day while you are away working. while you are working, you will be expressing and bringing home milk that your caregiver can use to feed baby on Tuesday.
Hope this helps.