I’ve just thought of a few more things I found useful backpacking, mind it was 30 years ago and S.E.Asia not Oz.
Sleeping bag liner, mine is silk and I still use it for certain types of holidays all these years later as I’m sure whilst the bedding is clean it’s a bit past it’s best in some of the more interesting places we stay and it just feels less ick to be inside the liner. Hardly weighs a thing and is tiny. One of the best thing I was gifted before we set off.
Backpack space - I massively over packed, as do the gap year-ers we host for a few days (live overseas expensive place) at the start of their adventures so I don’t think a couple extra kilos is here nor there, is life lesson you really don’t need that much stuff. I started with an 80litre bag almost as big as me and had soon swapped for 40litres.
Compression sacks the type sleeping bags come in, still use these to squish down clothing when travelling with rucksacks. Packing cubes don’t squish down as much are still useful for organising bits in pack. These are very light and take up no room and something you need more than 1 of.
Dry bags, another one always comes in useful in a different size. I suspect he can get in OZ but quality ones are pricier. Lightweight and don’t take up much room.
Advent calendar, I’d have loved one, now husband definitely not. I have seen small ones the size of a Christmas card.