Hard luggage is nice to have as it sits nicely on the bike and can usually be locked but you can tour quite happily without having to go to the expense of this sort of kit.
"Throw-over" panniers are relatively cheap, and available in a range of styles to suit most sorts of bikes nowadays, they may or may not be waterproof so packing your things in plastic bags first is always a good idea.
Rucksacks can be useful but NOT on your back - or your pillions back. They very quickly become uncomfortable, they restrict your movement and can also make the bike top heavy which will affect the handling. If you bring one, make life easy for yourself and strap it securely to the pillion seat (or rear carrier if you have one). Elastic "Bungee" straps are ideal.
Tank bags are useful for all the litttle things you may need during the day, camera, sunglassses, snacks, drink etc. Larger ones can take a surprising amount of gear, I often weekend with just a tankbag for everything. It can be lifted off the bike and taken with you too. Again there are many different types and styles from magnetic, to clip on straps, to complete fitted tank covers with bags colour matched to your bike.