If your work includes creative stuff, separate them into two: boring stuff – bills/contracts etc – and creative stuff for work.
For the mind dump/creative stuff utilise the "one in one out" rule. Design a box/folder/desk(if it's a bigger stuff) for it. And if you want to put anything in there and it's full go through them and remove which you don't need/are not good enough. It's a good idea to have somebody who's professional opinion you trust to go through them with you. They may see an idea which is worth developing even though you think it's worthless.
Of course there are some stuff – i.e ramblings – you just want out of your head. Feel free to ditch these at your own discretion. If you decide to keep them, think about if the emotions they bring forth are worth remembering or not.