Thanks for the therapeutic comments, everyone! Good to know I'm not alone. I don't have a lot of hats and we have four seasons, so it's definitely not a splurge and will get quite some use. And of course Icebreaker is usually lovely quality. Reviews said this was lightweight and small to pack but still fairly warm.
I got the backpack for my last birthday with the upcoming trip in mind and I'm looking forward to putting it to use in the coming years. I definitely liked this colorway best of the ones they had on offer! I tend to go for more muted colors and a lot of neutrals with my clothes, so picking a colorful pack seemed like a no-brainer. It's more visible too, which isn't a bad thing either.
If I have time I might post a packing list, it's going to be a fun challenge to manage the space I have available. I still haven't quite decided what exactly to take, but I have the most important things covered now. The Birkenstocks worked out great btw, I'm wearing them right now at home to break them in. One big decision I still have to make is what photo gear to take. I don't want to lug around too much and my DSLR is heavy, but this is New Zealand and Australia we're talking about here. I could ask my Dad to lend me his mirrorless camera set up which is so much lighter, but of course I'd have to do a crash course beforehand to get used to it... Not sure if I wouldn't regret not taking my own in the end (although the pictures you can take with his camera are great, too).