Where to donate goods/textbooks/items ~effectively in the UK/US/beyond?

Preamble: In the UK, I buy and sell used goods to Oxfam; in the US there is no equivalent. I tentatively proposed exploring such a store for causes even more effective than Oxfam.

I suspect Oxfam is an order of magnitude more effective than the other places I could donate goods (British Heart Foundation), even if it might be still much less efficient than GiveWell charities, and I don't agree with much of its advocacy. Oxfam also doesn't take many goods (furniture, electronics).

Q1: Are there any better alternatives to Oxfam for this in the UK, and anything remotely effective for donating/buying used goods in the USA?

I'm trying to donate a bunch of Economics and Statistics textbooks. At University of Exeter, there's a textbook drop for Hospicecare, but obviously that’s not a highly effective charity. I could donate them to Oxfam, but I'm not sure they will put textbooks online to get a good price; I suspect they end up as local dead weight.

Q2: Is there anywhere effective to donate textbooks in the UK or US? I could put them on Ebay individually for charity, but that takes a long time. The textbook merchants seem to sell these at about $80 each and buy them back at $0.50. So maybe that's their street value and I'm wasting everyone's time ... or maybe I'm missing something.

(Was hesitant to waste EAF time asking this question but at least 1 person +1'd it in a Slack so I thought I'd try.)