I don't share. I don't even like people touching my stuff. If it's a consumable item like candy or paper then it's fine, though I won't actively offer. I wouldn't have a problem with giving someone a pen if I had a box of them and wasn't in a situation where I'd immediately need one. But in school I had a weird anxiety issue with pens, so I was always worried about what would happen if I lost the six pens in my pocket and the three boxes in my bookbag, so I'd lie and say I only had the one I was using if someone asked.
But no lending of anything I'd want back. I don't like borrowing from others either.