We did avent bottles. And cow and gate formula - the midwife actually suggested it. in a "I'm not allowed to suggest a formula, but lots of the Mums I know use the one with the animal and the gate and don't have any problems" lol.
I didn't take anything into hospital, they provided little bottles that were ready and disposable teats that you just screwed on. They gave us a handful and we took a few home too.
One thing is - as soon as you get home from hospital, make up your first batch of bottles (or get someone else to) - we happily went to bed knackered the first night home, to be woken by a hungry baby and the knowledge that we didn't have anything prepared.
When my DD was little the advice was not to make up bottles and refrigerate them and I went everywhere with bottles of cooled boiled water and a dispenser for the powder. All of us Mum's did it - apart from the Mum who made up a bottle hot, then kept it in an insulated container so it stayed warm until the baby wanted it!
Not one of us had any problems with babies getting sick from germs in the milk, but I suppose the risk must be there as they've since changed the advice.
Now they say make up each bottle with hot water, then cool it ready for baby to drink. So for when you are out and about you are going to need a dispenser for the powder, empty sterilised bottles, a flask of hot water (filled when boiling so as sterile as possible) some cold water and a jug to be able to cool the made up hot bottles. Phew.
Pre made formula is expensive, but for one offs (like when we went camping and didn't want to take absolutely everything with us) they can be useful.