Woo, let's see. My compulsivity didn't show up until Oblivion, unless you count constant arrangement of gear on Chrono Trigger characters to make sure everyone had the most kit-appropriate items.
In Oblivion, I dedicated different containers in my house to carefully organized storage. A crate downstairs for weapons, a nearby barrel for arrows, an armoire upstairs for enchanted clothing, a bureau for armor, and a chest near the bed for special "memory" items - unique items like the handcuffs your character starts the game with, a set of Mythic Dawn robes from the first assassin you meet, leftover turpentine from the paint quest, the ring Vicente gives you, etc.
Additionally, my first time through, I had a downright obsession with stealing keys. My character had pickpocketed every NPC in the game, and stolen every possible key, and opened every possible door. I didn't bother stealing things from the houses, but I quickly realized that (due to the items lying around in the houses; books, weapons, etc.) some of the houses belonged to members of the Dark Brotherhood or Mythic Dawn, organizations I felt very strongly about.
I started carrying around a sheaf of Quills, a handful of Flawless Pearls, and two or three skulls. In normal homes I left a feather in a conspicuous place to indicate that I'd been there before; in Brotherhood homes I left a pearl, and in Dawn homes, I left a skull on the pillow of the bed. ;3
