Conventional wisdom has it that you should keep your rejection slips to remind you of how far you've come as a writer once you’ve established yourself. I’ve even read of people who proudly plaster their walls with the things.
Well, I came across a load of rejection slips whilst clearing our loft recently, and quite frankly I couldn’t wait to get rid of them. Call me an old hippy or something, but I really don’t see the point of keeping hold of anything that reminds you of your failures. Who needs that sort of negative energy dragging them down?
My advice: use the rejection slips as a means of improving your pitch, if the editor has been kind enough to give you good advice, but dump them as soon as you can take them to the nearest recycling centre.