A quick list of things to not put in with papers you plan to save for a long time:
- rubber bands, which either lose their elasticity, turn rock hard and crumble to tiny bits, or lose their elasticity, turn rock hard and adhere themselves to your papers like very determined barnacles.
- paper clips, which will oxidize and, if left long enough in the right conditions, start to eat straight through paper. Even staples can go bad. Stainless steel paper clips, however, are fine.
- tape. Fun fact: old cellophane tape leaves a crusty, brownish-yellow stain when the adhesive dries out. I have yet to figure out a way to get it to come off.
- post-it notes. As far as I can tell, the longer they are on paper without being peeled off and repositioned, the stronger the adhesive gets. By the time your friendly neighborhood archivist gets to them, removing them leaves a tacky strip that is more or less permanent. However, they are awesome for short-term use.
- three-ring binders, especially the kind with the clear plastic window on the front for a cover page. With laser-printed pages in particular, the ink gets stuck to the plastic both inside and out; I don't know if that's because the plastic is decomposing or the ink is. Actually, plastic of any kind is bad news, eventually.
- newspaper, unless you put some acid-free paper in between it and other types of paper. I have, while processing, come across documents permanently marked with the perfect brown shadow of the newspaper clipping filed behind them.
- receipts and other thermal paper. I just pulled some receipts from the late 1990s out of a drawer in our kitchen, and they had turned from white to neon yellow and all the black ink was faded beyond legibility. Fax paper (remember faxes?) just develops an even grosser, slimier texture than it had originally.
- rodents. You'd be surprised.
- insects. No, really, you'd be surprised.
On the other hand, a few things that may be helpful for you or whoever goes through your stuff in the future:
- keep two copies. Three copies, if you want a backup for your backup. It might seem like a good idea to keep a whole stack of, say, identical leaflets, but if you're not going to be distributing them, they just take up space. On the other hand, if you have only one copy of something, you can be sure a hungry rodent will find it.
- make paper copies. If there are e-mails to which you will want to refer in the abstract distant future, print them out. Floppy disks and CDs become obsolete or get corrupted. It is almost impossible to find a machine to read 5" floppy disks. It is remarkably easy to read a piece of paper.
- label everything. Someone else may not know that a handful of scribbled notes is actually the plot outline for the Great American Novel. You may not even remember twelve years later. Acid-free tabbed folders, labeled, are your friends.
- date everything. One of the easiest ways to figure out where something belongs is to date it and organize chronologically. Even noting when you received an undated letter could be helpful in the future.
- make box lists. If you're throwing a lot of stuff in a box for storage, take the time to make a list of what's inside. It doesn't have to be terribly detailed, just a bullet-point list you can throw in on top of everything else before the lid goes on. I can't tell you how much easier this makes my life as a processer when whoever packed the box tells me what's supposed to be inside. On the home front, if you're looking for something and don't know which box you put it in, having a quick-and-dirty inventory that's the first thing you see when you open the box makes the search go much faster.
- label photos. Label photos. LABEL PHOTOS. If a stranger goes through your photos (not in a creepy way, hopefully, but rather an archivist or genealogist), chances are they will not recognize your acquaintances on sight. In my own experience, it's hard to tell some of my great-uncles apart in their childhood photos, and it's hard to tell where family photos were taken when all living rooms looked alike in the 1960s. Captions help. A lot.
- go acid-free. If you know what you're printing will be saved for a long time (and you can afford it), consider printing on acid-free paper. A lot of scrapbooking supplies are acid-free, since the whole purpose is to preserve the photos and whatever else goes into scrapbooks, and I believe office supply stores carry some acid-free as well. It's more expensive, but in terms of conservation, it's probably the best option.
- avoid miscellany. "Misc." on a box means nothing. It reveals nothing. It is an enigma. And it's exasperating when you're searching your dimly-lit attic or basement.