insidious Clutter

It is interesting to me that very few people want clutter in their life (both tangible and intangible), yet it tends to manifest insidiously even for vigilant minimalists and requires the periodic clean-out to bring a space back into the desired state.

What is your insidious clutter that constantly tries to creep in? How do you manage it?

For me it's papers (bills and stuff waiting to be scanned) and children's toys (family just loves to buy my kids more and more junk). For my wife, it's stuff like lotions, shampoo, soaps, etc.

Our basic strategy is to give all this kind of stuff a designated amount of space they are allowed to take up, and once that space is full, stuff must leave before new can come in. We have a folder for mail/papers, bins for the kids toys (that have to be put away each day), and a basket for my wife's products.