TheDetective
Righto. Two scenarios based on the info you've given me
Scenario A - Using Staydown Formula
You're not going to be able to get cooled boiled water thru security. Nope. They'll make you pour it away or just give you loads of grief, especially if it's Heathrow.
Pack your 3 sterilised bottles. Pack a skinny thermos (eg 0.5L). Pack enough powder (plus your scoop) in a plastic tupperware box for SIX bottles (in case of flight delay etc).
Once you get through security, go to a cafe and ask them to fill up your thermos with boiling water. Measure out enough into your two bottles (ie so they can start to cool down ready for next feed) and get them to fill up your thermos again for the third bottle/fill third bottle directly. Now you can get the crew to do this on the plane with their hot water taps but to be honest it's just a hassle to get hold of them when your baby is hungry, so do it before you board at the airport. If your baby is hungry while the water is still very hot (it's hard to find a cold water tap in an airport to run the bottle under), then get a bottle of Evian or Volvic (ie low sodium mineral water) and mix boiling water and bottled water to right amount (usually half and half gets you to room temp) and then add powder. You're just going to have to disregard the 70 degree rule here for practical reasons.
Scenario B - Using Regular Formula
This is WAY easier! Ok, pack your 3 sterilised bottles. As for packing pre-mades, security are real bastards about this (esp Heathrow) and they could randomly let you through or make you open half, taste some etc. So what you need to do (aside from having a fourth bottle with a feed/carton in case you need to feed baby before security) is order your pre-mades to pick up at Boots after security. If you're going through Heathrow you can do it online - as for other airports, if it's not available online call up the airside Boots and ask them to reserve you some. You need to reserve 3 days before you fly.
Order 5 or 6 cartons - again in case of delays etc, getting to your destination at the other end AND FOR THE RETURN TRIP (unless you pack some in your checked luggage) in case you can't buy the premades you need in Switzerland.
For the flight back pack some powder in a tupperware in case Swiss security gives you grief about the cartons - but to be honest I've only found that UK airports are bloody stupid about them.
Generally For Your Trip
Some, not all babies get sore ears during take-off and landing. Start feeding baby (or give pacifier) as you're heading down the runway. If you're feeding, don't start before then or you'll run out during the climb.
If your baby likes bottle warmed, then the crew will do this for you. They are generally quite helpful!
Sterilising - you could do Milton in eg hotel sink/wherever you're staying. But the easiest and best thing is to get a Milton Solo Travel Steriliser - you can sterilise using a quarter of a Milton tab or in the microwave. Fits one bottle and a dummy, and your teat tongs. Cold water sterilises in 15 mins. It's bloody brilliant and saved my bacon, hands down one of the best things I have ever bought. I used it (along with a skinny Boots bottle brush and tiny bottle of washing up liquid) to sterilise DS' bottles easily and quickly in a aircraft toilet repeatedly during 35+ hours of flying. Also used it when DS was in hospital at 6 weeks.
Water - as I said above, you can use Evian or Volvic in a pinch to make up bottles. These are low-sodium waters so suitable to babies. Yes yes I know you are not meant to use mineral water and you are meant to boil it/70 degrees but when you are travelling you just have to be more practical (when the baby is hungry!!).
Pack one nappy for every hour of your flight. And 2 changes of clothes (based on your flight time). And a change in top for you and your travel companion. Trust me on this one. Babies, planes and poo explosions seem to go together