People are getting a tad hysterical over cows milk, aren't they, amirah?
No, cows milk is not suitable as a main drink for a baby that age but it is not his main drink! His main drink is breastmilk and he will be having a short four day break from it! Despite what formula manufacturers would like you to believe, this will be absolutely fine!
amirah, I have left ds3 and ds4 for periods between 2 and four days when they were still bf. On one occasion, ds4 was only 5 months old. On my return they both went straight back on to the breast without a problem as if I'd never been away.
You will need to express for comfort. In my case, I did bring a pump and tried to pump four times a day. I saved that milk and brought it back but that's what I'm like!
Your supply will not disappear in four days. It takes something like three weeks to get to the point where the milk does dry up and even then you could probably still re-lactate
FWIW, I brought ds2 and ds4 away before ds4 was walking. My advice would be to check in all baggage and bring the buggy into the cabin instead, if this is allowed. Otherwise it can be a bit of a struggle carrying a baby and dragging a suitcase and trying to control other ds. Ds2 was actually 11 at the time so was a help, rather than a hindrance but had it been ds3, I think I would have been in a bit of a bind!