When I was a kid, I remember talking with friends about burying a time capsule. How cool it would be to bury something and dig it up a few years later. I don't remember if we actually followed through, but I'm sure there are remnants of our childhood underground somewhere.
This came back to me recently when the city of Tulsa, Oklahoma, reclaimed a cache of items that had been buried 50 years earlier. Among the items buried was a 1957 Plymouth Belvedere. As you can tell from the picture, the Tulsa capsule, which was designed to withstand an atomic blast, apparently couldn't deal with Mother Nature and her "gift" of several feet of standing water.
Now comes the current rage of geocaching, where people hide items to be found through various clues, a modern-day version of a treasure hunt. One offshoot of this is geocapsuling, stashing a family's memories in a fake rock to be discovered later.
Since I have doubts that my descendants will take the time and trouble to hike through rugged terrain to uncover bits of my family history, I prefer a more direct method. But, maybe you come from more adventurous stock. If so, you can check out Time in a Capsule.
Whatever method you choose, make certain your efforts don't come to the same sad end of the 1957 Plymouth.