I have the perfect method of storing 10 years worth of rares, mementos, bric-a-brac or whatever the hell the kids are calling it these days.
On one account, no less, in one house!
Whenever I see my storage space dipping below 100, I go through everything and determine what I don't need any more and sell it or throw it away.
Here are some of my decisions:
Item: Entire Holiday Bust Collection
Rationale: 5 Years Later, they still aint worth a Pickles' Nickel.
Space Recovered: 86
Item: Countless Event Items (Vorpal Blades, Twilight Lanterns, etc)
Rationale: I need one of the item for my posterity collection, and one more should I choose to sell it later. The rest can go.
Space Recovered: Thousands.
Item: Holiday Tree
Rationale: It's obvious OSI is gonna give it out every Xmas anyway (incidentally the only time you can use it), so it's utterly worthless.
Space Recovered: 20
Item: Hoarded Flour and Foodstuffs.
Rationale: I made GM Chef. Food is also pointless in UO.
Space Recovered: 50
Item: My Mage Scroll Collection.
Rationale: My mage has all the spells in the spellbook. My other characters dont use them.
Space Recovered: 30
Item: Soulstone Fragments
Rationale: I have three Soulstones. I'll never need more.
Space Recovered: 23
And so on and so on.