- 100ml ice bricks. The smallest we've seen so far are 150ml. When you travel without refrigeration throughout the day, an ice brick can be extremely useful to keep food cold for longer.
- quick-dry breathable kids clothes (at reasonable prices). You can get all manner of quick-dry clothes for adults, but nothing for kids. There's only so much beachwear you can have your kids in before it looks really out of place. For dining out, rash vests don't really cut it. Similarly, some sights such as historic churches require long pants and covered shoulders - items lacking in kids quick-dry clothing ranges. You would also think that manufacturers would be making quick-dry underwear for kids - but they don't.
- 100ml concentrate washing powder (or liquid) and stain remover. Getting a huge chocolate stain off a t-shirt in a hotel sink can be a struggle without it. Yes, I know that supermarkets are everywhere, but we don't need to buy (let alone lug around the countryside) a huge quantity of it. We tried to take a small bottle of washing powder on our last trip, but it was confiscated at customs because it was detergent, and therefore not permissible in the aircraft cabin.
Many toiletries are irritatingly just over the 100ml limit. We found toothpaste, sunscreen, moisturiser, shampoo, conditioner etc. at about 120ml. So close, yet so far. We did find the toothpaste and the sunscreen at or under 100ml, but all the rest we packed ourselves into individual empty bottles.