What should I provide if I rent a car in Spain but my driver license is Australian ?
Your Australian Drivers License is OK to rent and drive a vehicle in Spain. And you will need a Credit Card (some suppliers accept a Debit Card).
You can always get a digital IDL if you wish , it is always useful in certain countries. IDL - You can obtain a downloadable digital copy of an International Driving Licence here:- https://e-ita.org/
So would you just accept my driver's license + debit card? And how much is the bond if I take the full cover insurance?
Yes, the bond ormally is 300 EURO or less.
So do I just need my Australian driver license and my debit card ?
In case of a Debit Card: Make sure you choose a supplier that accepts a debit card using the Debit / Credit Card filter ( click on the link to see a screenshot of that filter ): https://v2uploads.zopim.io/4/O/U/4OUR3Pm9veURcpuPQf5b0xlskLAgHhdX/8151c5e0d7288dbd845a4bfee66bcb2f3b329407.png