One of the things that is taking up a lot of research time is the concept of Ragnarok Proofing - quite simply, making things able to last:
a) catastrophes of as wide a variety as possible
b) time.
Of course, making things to last a long time is difficult - the trick to Roman cement has only just been discovered, many centuries after it was last used - but has lasted all that time, even in marine environments. Compare that with (as previously mentioned) modern cement, which would likely not be left in one century, particularly if it comes into contact with water.
The other factor, that people don't necessarily remember is:
c) can be replicated, and not left secret.
I've been spending my time amassing a library, as some others, but is that library of much use if it is predicated on there being certain machinery still working? Having lots of books on computer chips is great - but if those chips are no longer available, say a hundred years down the track, are your descendants going to find those books worth worrying about (and that's if those books last that long)?
You really do need a community in order to last the years...
On a related note, I think I've come up with a possible process for creating ice PSHTF, just using wind power. Of course, making a proof of concept version is going to be a pain... I need to find a reliable source of funding for such technologies, I really do...