This trip is going to be great. Your intuition is mostly right on, in terms of packing. Here's a few small things you'll wish you brought.
- Hdmi cable. It's fun to watch movies in hotel rooms, and you're going to want to connect your laptop.
- All your and the family's favorite movies, downloaded as mp4, on a big USB key. This is annoying and illrgal to do at home, but take the time and do it. Streaming sucks everywhere. All the TV's have a USB port. Tie a huge ribbon on it, because you will forget it.
- Variety pack of screws, washers, bolts, and small tools screwdriver tip. You'll fix faucets, doorknobs and shelves at every guest house you're at. Airlines don't care if you bring the one with removable tips.
- Food bag. You don't want to lug one around, but you'll wish you had a thin insulated bag that closes well, with pockets for yogurt etc. I haven't seen one perfect, but look for one.
- Roll-on bag with no backpack straps. You were right: This bag is too small, and you're not going to be wading through rivers like REI likes you to think. The straps take room you need. No one cares if you look like a city slicker.