Suggest the best Amazon bargain for £20-40

So I did an old school survey recently that was left at my door by Ipsos-Mori and for my troubles I was given a £20 Amazon voucher. It is burning a hole in my proverbial pocket and so I thought I'd ask people to let me know their best recommendations for products that are a total bargain. Obviously under £20 and it's a completely free item but even something at £40 I'm getting 50% off - what are you saying HUKD?