One more from the wise folks in the 43 Folders Google group, here's Vicki Brown:
Ask yourself –
if I lost this, how would I feel?
do I remember having this?
does this item give me any good (or bad) feelings?
do I know someone who could use this?
Sometimes I put things in a box or a file folder for a while. If I don't go back and retrieve them, I know I can get rid of them. My Dad used to clean the house like this. He'd toss things into boxes and take the boxes to the basement. If no one said "Has anyone seen my _______" after a month or two, he'd toss the boxes.
Do you have a chapter of Freecycle where you are? If you feel that someone else will get use out of your "stuff" you may feel better about getting rid of it. Or, Salvation Army, Goodwill, other charitable thrift shops will often come get things. No extra work for you, nothing in the landfills, and maybe a tax deduction.