The interstellar part of the Voyager missions included a disk with various information about our world on it in case an intelligent species happens to run across it. That way they could come say hi if we were still around, and at least know we once existed if we'd destroyed ourselves by then. A quick summary of their progress:
"Voyager 1 will drift within 1.6 light years (9.3 trillion miles) of AC+79 3888, a star in the constellation of Camelopardalis. In some 296,000 years, Voyager 2 will pass 4.3 light years (25 trillion miles) from Sirius, the brightest star in the sky."
If we're willing to wait a couple of hundred thousand years for someone to open the time capsule the least we can do is make sure the information in it is current. The way to do this would be to create a Voyager 3 and park it in one of the two stable Lagrange points (L4 or L5). If it was solar-powered it could hang around for quite awhile. We could also send it updates as our civilization progressed.
Another thought - it could start beaming back information to us if it hadn't heard from us after a couple of thousand years. That way if we bombed ourselves back into the stone age we'd start receiving a steady stream of technological information to get us back on up on our feet faster once we'd got back to the point where it looked like civilization was starting again. In order to help us along Voyager 3 would have to be able to do two things:
1. It would have to be able to spot a pre-industrial culture while it was sitting at one of the LaGrange points. It could do this by looking for evidence of artificial structures on the surface - straight lines, clustered buildings, pyramids, statues carved into mountains, etc.
2. It would then have to be able to communicate ideas to this culture without relying on radio (since that wouldn't have been invented yet) so it could steer them towards development. The easiest way to do this would be by sending a lander near one of the settlements and then projecting images of the lessons it wanted to teach. The lessons could either be shown automatically on a screen that came with the lander or, if we reach the point where we could project free-standing holographs, we could have a holograph disguised as one of them show the lesson. Done correctly, it would look like a vision to whoever saw it.
Once they reached the point where they had radio again our computer would have to either learn their language or teach them ours to communicate more advanced concepts. Medical, mathematical and technically sophisticated information along the critical paths of invention/discovery could then be sent. Some of the less critical solutions could be left out leaving the revived generation to discover then on their own (giving them the chance to arrive at different solutions to similar problems in areas we could afford to risk).