Here's a smart way to make an extra buck or two. All you need is to live in the UK and have a smartphone. You may already be familiar with musicmagpie and you may already have tried to shift a number of CDs, DVD's or games and received 30p for them because they are popular titles? With a little effort though, you can actually make money from the site.
I've found this only really works with CDs and you need to have a bit of music knowledge for it to work... or to save time at the very least. Many charity shops in the UK sell CDs for £1 or sometimes even less. By downloading the musicmagpie app onto your phone you can scan barcodes in shops and see what Magpie would offer you for the title. The trick is to hunt out the things that look obscure. Anything populist isn't going to make anything but I've found small independent releases can sometimes fetch £2+ as can smaller label classical music releases. It's a bit of trial and error but can make you £10's if you invest some time and know what to look for. The most you can make from musicmagpie on 1 x CD is £3.00 but find the right disc and you can triple your money.
Please bare in mind that musicmagpie can take a month for the money to come in. Discs also need to be in good condition with few scratches for them to accept them. Also any artwork needs to be undamaged (and this includes holes or lines through barcodes).
If you find a few shops that reliably stock good CDs then money is there for the taking.