Medium Hassle Involved
This involves you taking the stuff to the shop, though if you have a local one it might be worth asking if they can collect. You might want to avoid some of these if you are not happy about testing on animals.
Also, some of the bigger charity shops have a reputation for spending more money on shops and management than on the charity. Oxfam is famous for this and the RSPCA are said to destroy half the animals they rescue. This article in the Independent says “On average, 3p of every pound you spend is soaked up in the expenses of running the shops” Personally I try to give my stuff to smaller local animal shelter charity shops or to places like Emmaus who help, home and retrain homeless people. My local one takes clothes and books as well as furniture.
You can sell your old books on Amazon for free, the listings stay up as long as you like but you do pay a commission when they sell. This is pretty painless because all you have to do is type in the bar code but then it’s a hassle packaging and posting them out. The best thing I think is to check the prices of your books on Amazon first then just sell the ones that are going for the most, ones that sell for 50p you might as well just give away. The only problem with this is that you will have a box of books waiting to be sold and this could take some time.