Nothing.
Apart from insulation and bits of plumbing which are supposed to be there, there's nothing in my attic. I learned my lesson when I had to empty my parents' attic after they died. The access was dangerously awkward, most of the goods had been spoiled by damp, the rest were worthless. It took ages to clear. So I decided I was not going to do to my offspring what my parents did to theirs.
Suitcases and holdalls; 2 bookcases full of books; a set of drawers full of my magic DVD's and books; old PC (still works, but not used) along with computer table and chair; new printer (currently in use); several boxes full of odds and ends .....
Mind you, it helps having a loft conversion though - I wouldn't like to have to keep climbing a set of ladders to use my printer :)
Christmas stuff, a tent, pictures, pots and the remains of a squirrel's nest. I was thinking of having a proper loft storage room done but I won't be here long enough for it to be worth the financial outlay