Just travelled from Mexico to Illinois and back this past September, with my four kids under 4 (yikes!) We took so many sandwiches and ate them all! Seriously, get two loaves of bread, then make all the bread into sandwiches, and then place the sandwiches back in the bread bag! Genius! A little heavy at first, but they get eaten, so no problem. We also had each kid take their own backpack full of coloring books, reading book, and crayons, that way I didn't have to dig through my own carry-on looking for stuff.
Oh, and we used leashes (diy, just a thin rope attached to a carabiner) attached to their backpacks, but with just one you probably won't need that. Definitely useful when your hands are full taking care of passports and stuff.
Make one adult your passport ticket person for the whole fam, and then other adult can hold your kid.
It'll be a breeze and tons of fun!
ETA: I hate leashes, and imagine others do, so just to clarify, we didn't use them all the time, just at points where it was necessary. We had to stand in line forever going into customs in the US, and we had a suitcase and a stroller in addition to the three preschoolers. We used the leashes there a bit because the kids can easily slip under the line-thing and just...wander away.
Also during ticketing was helpful. Also helpful just as a choice, like "hey kid, do you want to walk right next to me or do you want me to get the leash". But again, with 1, probably not necessary.
Oh, I should add that it was definitely helpful having only one suitcase!