One that has inspired two stories from me recently:
Hoarding. Our characters pick up a lot of random items on their journeys. What will they never throw out? What if someone wants them to have a clear out? What happens when they run out of space in their packs?
My characters definitely display hoarder symptoms. I don't keep everything, but in my last game I had two full bags of holding, a scroll case full of books, a gem container full of rare gems, rings, necklaces etc. an ammo pouch for all my rare ammo, and most of my party had pretty full inventories. I tend to drop or sell the really common stuff, but I like hanging on to all the unique equipment, one of a kind items and all that kind of stuff - even if my party has no use for it. Sometimes I'll even hang on to old keys and empty potion bottles!
Skyrim has been just as bad - I keep almost everything in my houses. I just chuck stuff into containers and leave it there. Last time I checked, I had three complete sets of armour just sitting there.