Books: I go through those, the stuff I've read and will not read again I either take to a local used book store and trade them in which gets me .... yep, more books or drop them off at the local library for their book sale.
Excess sheets, towels I drop off at the Animal Shelter. They always need them for bedding.
If you have excess furniture here's an organization to donate to:
www.furniturebanks.org
This is mostly California but a ton of useful links:
www.stopwaste.org