My DD3 also is lactose intolerant, unfortunately I never saw soy or lactose free anything. She just got a juice box of apple juice everywhere we went. I was in a fridge swap, so we went to wal-mart twice to get lactaid milk, everytime we left the room, I filled her sippy cup with milk, so she atleast got some twice to three times a day.
My doctor said we could give her half a lactaid once she turned 2. We actually started at 18 months and never had a problem, other than loose stools. The lactaid stopped all the cramping she had, and kept her bottom from being so sore. If you haven't heard of Happy Hiney, get a prescription from your peditrician. It is desitin mixed with a topical pain killer, which soothes a sore bottom, and heals nasty rashes within hours. My DD3 still will occasionally ask for it!
This is tough to deal with, but you'll be alright.
I think in the end, this was great for us. She never had all those foods, that kids only want to eat, like mac n cheese, most all canned foods, etc. She eats fruits and veggies mostly! It is tough telling her she can't have cake, ice cream, all the fun stuff when other kids are eating it in front of her. She just now started saying "that will hurt my tummy?" She understands. I let her have a lactaid about twice a week and have a treat.
You could keep him on soy formula if he'll still drink it when you go. Just pack some powder and you can always get water. Also they have soy milk drink boxes that don't need to be refridgerated in the market health section in the grocery store. After a while you'll learn the brands that don't use milk, whey, butter. Pillsberry icing in the jar is made from soy!