Time capsule for 2057, you say? Here are three things I'd throw in.
1) The Tower Records sign. It might be a more relevant artifact of 1980 than 2007, but at least it's still meaningful to many of the people that watched the chain close this year and divebombed the liquidated stock with glee. This entry comes to me as I sit in Dialog Coffee & Bakery, across the street from the erstwhile Sunset Strip Tower, temporarily rechristened Icky Thump Records as a promotion for the White Stripes' new album.
2) Comedy clubs (well, just one for posterity). A concept that hangs by a thread after somehow surviving into a new century, as Tower was before those final days. Every one I pass now looks so worn and sad, secreting desperation from every crooked letter on the marquee. Along with our comedy club we can also bury a homebrew DVD-R with footage and news coverage of Michael Richards' standup meltdown.
3) Circulars (the ever-present print advertisements and coupons that clutter up our newspapers and mailboxes). I'm hopeful that 50 years from now we'll be inching closer to the paperless society we were once promised, and businesses can learn to be less wasteful, saving some money and some trees in the process.