The items you must obtain at all costs.

[Scythax]

I have a strange compulsion every time I play Oblivion that evenever I see a bookshelf I MUST slash every single book onto the floor or shoot a fireball at it to make them fly everywhere. Anyone else do this?...No?...Ok then.

In fact I do a lot of random stuff in Oblivion. I once got a massive collection of every skrunched up piece of paper in the game (ended up with like 78-79) and dropped them all on Martins lap in Cloud Ruler Temple, and then just left him there for the rest of my game, covered in paper balls. Cracks me up every time I see him like that, talking to people with a huge mound of them on and around him as if they arn't even there.

 

[ottenni]

Ammunition with yellow stripes on it in STALKER Shadow of Chernobyl. I can never have enough. NEVER!

 

[Cody211282]

Everything I can get my hands on I grab, games like ME and DA:O I need a lockpciker with me because passing up stuff is not an option, also it drove me insane in Fallout 3/Oblivion because I didnt put anything into lockpicking for a bit

 

[AWAR]

Every rare-unique item in oblivion

 

[Lazy Kitty]

Pokemon, though I never succeeded at that.
[sup]Not yet anyway...[/sup]

 

[Reire]

I tend to slowly stock up on ammo on RPG's, got an insane amount of useless arrows on Oblivion

And the R.Y.N.O on the first Ratchet and Clank, the ones on the other games were far to easy to get though

 

[Kajt]

I pretty much pick up anything I come across in games like Diablo and Torchlight.

[sub]It's a curse![/sub]

 

[SangRahl]

I'm a notorious packrat. Essentially any RPG or MMO will leave me begging for more inventory or pack space and/or crawling across the landscape with weapons, armor, treasure or plain junk to sell or stockpile... and don't get me started about player fashions (like having a bag dedicated toward disguising my old WoW rogue as a caster to get the drop on less-situationally-aware players in PVP and duels).

My best/worst example would have to be Fallout 3: Still barely 3rd to 5th level (depending on my playthrough's build or current mod setup), and nervously scanning in 360degrees for threats as I slowly trudge back to Megaton with every scrounged piece of armor, weaponry or viable piece of salvage from S-D Mart. Every playthrough, I'll end up with enough material to build a dozen Rock-It Launchers (though I've never actually done so, or even used one for that matter). One character had a collection of every skill book and Pre-War book he ever came across displayed on his apartment bookshelves.

Then there's the whole deal with what I actually USE for weapons/armor... both for my characters and my companions. I've done the whole vanilla armor progression from rags to full Power Armor, and in the end I preferred having style over optimized performance. And, once I'd discovered modding, having a custom reinforced leather jacket (addorned with raider spikes) for my melée brawler, jacked-up BoS Power Armor (with recon helm and silver pilot's glasses) for my "I love the smell of cordite in the morning" heavy gunner, and my underworld enforcer decked out in full Mod Squad threads (nothing like having Charon and Clover in full Pre-War Business attire with matching combat shotguns, or maybe Jericko in a duster with a Winchester).

In the end, I'll have stocked up on piles of books, componentry, and every custom weapon and armor I come across... regardless of whether or not I'll ever plan on using them. This scenario is repeated in just about every game of the like... spilling over to the same obsessive collecting in pretty much any game that allows for the practice.