We have travelled aboard with both our two kids when they have been babies. We travelled to the Philippines with our oldest when he was 6 months old, and we are just back from Morroco and our youngest was 5 months on the way out. The Philippines flights were all with Cathy Pacific, which made it fairly easy as we had bulk head seats with a small cot (skycot)to put the baby in - as long haul flights go they were actually pretty easy. In comparison Morocco was on a charter flight with a baby on our lap for 3.5 hours, while it wasn't too bad it was still a bit of a squash, especially when the food was handed out.
As mentioned in post above Medised is great, but it is no longer recommended for babies.
We have found the health care is often better abroad than it is in the UK, if you want to travel it is really not a reason not to go.
The current situation with bottles of water or milk on the plane is you are allowed to take them, but you will be asked to remove the top and drink from the bottle. They also swab the bag it is in to check for explosives. I would imagine that you would have any cartoons of milk taken off you, however you can buy these at Boots once through security.