I'm a huge fan of his Discworld books and am the proud owner of every single one! Plus The Discworld Mapp, The Streets of Ankh-Morpork map, A Tourist Guide To Lancre: A Discworld Mapp, The Pratchett Portfolio, The Art of Discworld, Nanny Ogg's Cookbook, The Discworld Almanack and The Folklore of Discworld :-)
As well as being a fantastic author, Sir Terry was an all round awesome dude. He campaigned for assisted suicide, raised awareness for Alzheimer's, and was a trustee for the Orangutan Foundation UK.
He also had a greenhouse full of carnivorous plants and made himself a sword!
I have some Discworld artefacts from The Discworld Emporium. The crowning jewel is my The Turtle Moves pin, which the website says was designed by Sir Terry himself to function as "a symbol that would tell one Discworld fan to another that they shared the same taste in literature."
I also have some Ankh-Morpork half dollars, in case I ever visit!
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Here's to you Sir Terry, you are greatly missed.