If you want to continue breastfeeding your child once you go back to work, you need the whole bottle supply chain:
- A pump
- Plastic bags to freeze pumped breast milk
- Many women recommend a photo of your child that you look at while pumping. This releases some hormones that support the 'milking' process
- Equipment to keep milk pumped at work cool until you can freeze it (fridge, or cool packs)
- Equipment to unfreeze/heat the stored milk (a pot with boiling water works just fine, but there are also solutions especially for this purpose - for a price, of course)
- Bottles and nipples
- Bottle and nipple sterilizer (a pot with boiling water works just fine...)
How do you prepare for it - well, I suggest practising all the steps involved some weeks before you actually go back to work: The pumping, the freezing, bottle sterilization, unfreezing, heating, and bottle feeding. Try to make the situations as close to reality as possible, for example pump when you are not at home, and your baby is away, have someone else give your baby the bottle while you're gone etc.
That way you will discover all the things that are missing in the list above, and what can go wrong.