I keep all the boxes, product packaging, accessories, and receipts for all the Apple products I own or anything else electronic I think is important (mostly everything that is important). Why? Because it makes it much easier to return (if needed) or pack up (if needed).
Scenario: Your PS3 breaks or XBOX360 gets "red rings of death". You call for warranty confirmation from Microsoft or Sony/Best Buy (if you use them for Geek Squad, etc) you pack it up nice and neat (because perception and presentation play a large part in reality - think about that one) and take it to the store for a return/exchange. It takes an extra couple of minutes both at your house and at the store to get a look at everything but it's worth it. The reps say "Looks like you took care of everything." "Man, you're PS3 is in great shape, what happened? Doesn't look like it was damaged." Things like this make your version of what happened more believable (not that it wouldn't be true) and a manufacturer's defect or whatever. Compared to the person that just lugs in all their crap haphazardly, wires falling all over the place, nasty dirty piece of equipment, lays it on the countertop and says: "This is broken, I want a return/exchange." They don't have anything with them, not even the receipt. Pain in the ass for the store, pain in the ass for you.
I've seen it happen and it's ridiculous. Anyway...