I know I am just tempting Jeppy to have one of her fits, but I will chime in here.
Let me say this: I really dig this thread! Such great info, ideas, and experiences. Dig it!
So I have a darned good sized (just barely carry-on) rucksack I took to Argentina and Uruguay. I take that because it is rain resistant and has built-in covering to make it nearly rainproof on top of that.
I put some basics in there like clothes, toiletries, and such. No need to go into that. I will however mention the perhaps out of the ordinary items I take.
Several ziplock freezer bags, little ones and big ones. They have many uses and if you lose them, no big deal. They are submerge-able. They are durable. They also keep funky smelling stuff away from clean-smelling stuff. Helpful when you are living out of one ruck sack!
Inside the ruck sack I take a collapsible little ruck sack for day trips and such. Very handy!
I also have a waistband wallet with cash -- extra cash.
Obviously I keep it very minimalist all around. So there you go!
The lifestyle of the jet set loan drones!