Pens, oh man we had millions! I sent a huge envelope of stationery to some charity thing in Africa and still have enough to take into work to use! I work in a firm with over 200 people, there is no shortage of pens but I just couldn't visualise when I would run out of pens if I only use them at home.
3yr old DS is keen on drawing and writing his name (ahem, on the paperwork pile to be kondoed, not that I need anyone's birth cert, oh no).
My solution has been to keep any remaining pens in the stationery drawer in the kitchen (cut down cardboard box contains sellotape, gluestick, post-its etc). The pens are in one of those boxes with a dimply sort of button that has to be pressed in to open it and DS hasn't realised how to do it (yet)!
I also have a pen in the top pocket of the wrapping paper bag which hangs on an S hook in my wardrobe next to the little drawers I keep greetings cards in, so I can wrap and write without going downstairs!
DS's crayons/felt tips/playdoh all live in the awkward corner bit of the kitchen cupboards, hidden by my huge tub of Tupperware. This avoids any walked-in playdoh and wall-scribbling incidents because only a grown up knows the secret location of the crayon/playdoh box! Muhaha!