Fountain Pens!
Vintage, new, cheap, fancy, flex, stub…I love 'em all!!!
Maybe even better than fountain pens is INK!!
I love ink. I have a couple dozen bottles and ink samples galore!
I have the multicolored 7-pack right in front of me. 
The Pilot Varsity is a remarkably great-writing fountain pen for the price. (appx $3) I normally use one of my “better” pens, but I keep a bunch of Varsities around my desk. We can actually get them through the office supply catalog, but only in blue, black, or purple. This 7 pack is my own. I was just feeling frivolous today. p.s. They are refillable if you know the trick.
And for those of you who like staple removers: Stapler Removers – Jac Zagoory Designs
The things I currently use the most are acid-free foam core, Elmer’s glue, rulers, single-edge blades and Xacto knives.
When I was a kid, my favorites were boxes of colored pencils and crayons, the more colors the better. I still have every color pencil made by PrismaColor.
I love Pilot Precise v5 black rollerball pens. I buy a package of them and just rotate between them.
And blank books. Notebooks, sketchbooks, any kind of blank books. I have a drawer full of them. My favorites come from Barnes and Noble: medium-size spiral bound notebook with different colored sections. I just love the way the paper feels. I buy these things two and three at a time and just keep them around the house.
Oh, I forgot Post-it Notes. I use the 2x3" which they haven’t made in years . . . but I stocked up on them and will probably never run out. I keep them all around the house and car and in pockets, now that I can’t remember things like I used to.
You can get a 2 pack of these at most office places for about $1!
Mine is notebooks. I’m a list maker, and a planner, and I love nothing more than a fresh spiral notebook with a pretty cover 
I’m also a big fan of fun colored pens.
I love a brand new spiral bound notebook. I keep a notebook handy to jot down ideas and lists and I use every page till it’s full, then start another. They are kinda like journals, but without all the writing and deep thought.
I also love Pilot G2 pens. They are the best!