We are off on a holiday next month: first time with the baby - who is only on formula feeds at the moment. Not sure what all to carry besides formula, bottles....should I rely on microwaving the bottles in hot water at our holiday apartment or carry a portable steriliser?

A portable steriliser isn't very bulky - try the Pigeon compact steam steriliser. Otherwise, you can get sterilising tablets to save space. You just need to fill up a container with water, place the tablet in and soak the bottles. It's very convenient. I wouldn't use a microwave machine as well.