No luggage needed...
Remember these are little boys traveling together. 1 set of underwear will last 4 days.
Day 1. clean set.
Day 2. switch front to rear.
Day 3. turn insideout
Day 4. switch front to rear.
Then, Bernie says, we will switch off. Gotta love the inventiveness of the Aussies. Now you get 8 days.
As for washing them? Any puddle will do.
So therefore they can get 8 days out of a set of underwear. The same for socks. Only you have to switch feet.
Mike