My brother and I put a corked glass bottle down in an old defunct drainage pipe beneath my parents' house. This pipe/canal is quite large and isn't obstructed by the bottle, and the bottle can clearly be seen by peering into a hole in the cement of the basement storage room. Inside of that bottle is a carefully folder paper bearing on it a crude drawing of a cock and balls.
A stack of Freshmen magazines with the address labels torn off, along with one woodworking magazine. People love discovering old porn. It’s like a gift to the future.
Place photos and some small objects maybe even a usb key, dvdr or cdr with a video of you explaining everything and telling the viewer who you are, what year it is, what's going on and what's important to you right now. Place it all in a water tight container, maybe even an iron case and weld it shut.
If you have small kids, tell them what you're doing and show them .... maybe they or their kids or your descendants might dig it up some day.
Of all the places I've renovated, I would have enjoyed finding something from someone else's life.
Stuff from different decades just to confuse whomever finds it. Like get a Five Stairsteps album from a used record store, a Blue Oyster Cult 8 track, a Tecmo Bowl cartridge, a Boyz II Men CD, and a newspaper from yesterday.
Write a long ass book that's filled with stupid stuff like "Fear not for I shall return from my deep sleep in 4*10^6 years and give the heavens (a bunch of virgin girls) to those who I find worshipping near the ground of this very hole you find the book I sent you" and toss it in.
DO NOT return in 4*10^6 years otherwise you wouldn't have trolled the entire humanity.