Hi L. -
She feeds her son Jr. Lunchables for DINNER? OY, what a lot of salt & fat!! Sorry, that sounds judgemental -- don't mean it that way, just genuine concern. I do give in and let my daughter have those rarely (she's 8 and she's had 2 of them in her life).
Anyway, I have 2 suggestions: one, you'd need an insulated bag and something like blue ice bags. Have little "plops" of whatever you've cooked/pureed (I use to do that; I'd freeze them and have them in a container or a ziploc). You don't say how long you'll be there, but you could pack quite a few and they'd stay pretty cold. Depending on how "frozey" they are when you get there, you can either put them in the freezer or the fridge (you shouldn't re-freeze if they've thawed). Honestly, that sounds like a bit of a hassle to me, but if you're a real purist, you can go with that. Or, even better, you could always pack a food mill and grind up fresh cooked for your baby boy. OK so that was suggestion 1 and 1-a.
Suggestion 2 is pack organic baby food that you can pick up from Whole Foods or Wild Oats. Actually, reg grocery stores probably carry it by now too. As I said my kid is 8, so I haven't been paying attention in the last few years. Or, even better, perhaps there's a store nearby your SIL that would have org baby food you could buy? I think the brand I used to buy is Earth's Best. It's not fresh, but heck, when you're travelling, you need to have it be a bit more simple!
Be prepared for some eye-rolling --- my dear sister with 4 kids was over it by the time my daughter came along! She thought I was a total fanatic! But you should see my daughter's immune system, strength, & stamina! (I am willing to admit that might be genetic -- but I'd like to take some credit for feeding her very well).
Have a wonderful trip!
Colleen
ps -- you know what? you should probably check with the airline to see if you can pack food, even in store-bought jars. You might end up having it taken away from you. A food mill is prob the simplest, lightest, easiest way to go! I guess I take back most of my suggestions! LOL!