I hoard all the unique items I get my hands on with the exception of some that just use regular meshes because I can always enchant something better and name it the same.
I have to have 1 copy and only 1 copy of every book I run across.
Like most of you I hoard things that are useful like food, alchemy ingredients, potions or soul gems, but I have mods that let me combine some items into more powerful versions. I play a magic user 99% of the time, so I tend to get rid of potions unless they are health, magic, or that insanely powerful jarrin root poison.
If modded armors with unique meshes count, I hoard those too. One of the first things I like to do is get my smithing to 100, but that's because it lets me get access to my modded armors without having to remember their names to get them through the console.