First, I love that little backpack that surely takes up little space in the travel lugagge and then can carry what is necessary for a walk. I had the idea of buying one so that it doesn't take up so much space in my bag, but it only remained in that, in the idea ;( I need one asap.
And second, amazed at that Octopus card haha. It's great that it's multipurpose and you can pay for everything, including transportation, and now also with your cell phone. Even easier and save having to carry cash on you.
Here in Buenos Aires, Argentina, we have the traditional Visa debit cards and to a lesser extent MasterCard for general purchases in malls, stores, eating out, movies, etc. We also have a card to travel in public transport called SUBE: you load it with credit and it works like a debit card but only for train, bus and subway transport (taxi only accepts cash, then UBER and other transport by car apps accept cash and credit/debit card). And we also have virtual wallets to pay from your cell phone, the most common being Mercado Pago, with this you can make transfers, pay for services, buy online or in physical stores with QR; all using the cell phone. You can also ask for the debit card but nobody uses it.
Having said all this, how nice it would be if all this was unified in a single system 😂. You're very lucky :p