Okay,

I have old textbooks from Uni and since I did Physics with Astrophysics they're of a technical nature. They're also not really out of date. There'll be a few changes, no doubt, but much of the stuff we had to learn was 19th Century or older ideas that are still true.

So my dilemmas are:
1 - do I keep them as the sole repository of the knowledge I should have retained but clearly haven't
2 - if not do I:
a) charity
b) ebay/Amazon marketplace
c) is there some better way to pass on such items?

For all I know Manchester are still using them in courses. I have a fair few of the Manchester Physics series in the second edition (turquoise covers).

And they're almost all published by Wiley.