I briefly looked through two guides, and neither one seemed to have a topic that stood out and said stuff about the rucksack. And the two little squares that hold things can't be all that you get for the whole game. :-| So my question(s): Can you upgrade the rucksack? If so, how? And by how much?
You can upgrade the rucksack twice, much like your house (but not really.) Go to the supermarket (where Karen lives) and go to the far right. There should be a counter with a backpack on it. Buy it for 3000G. (Now you'll have 5 slots) Then, wait a week and go back to the supermarket. There should be another rucksack on the same counter, in the same place. Buy it for 5000G. You now have 9 slots total, including your hands. Tadaaa! *gestures widely at nothing*
*Kricket "Keep smiling, it makes people wonder what you're up to."