Literally anything. You don't need a specific prescription. It's just a 'bonus' of being pregnant - whatever you might ever need a prescription for while you're pregnant (and for some time after), you will get for free. Doesn't have to be pregnancy related. You just won't have to pay for any and all prescriptions
Last time I was pregnant I got free Gaviscon and my godddddd did I need that later on...
Any prescription you require until the end date and NHS dental is free