This gets posted a lot and I'll admit I did post it last year after buying it as a Christmas gift but it's even cheaper than what I paid for it then.
It makes a great stocking filler. Don't forget Quidco / Topcashback.
Simply attach a WaterBuoy to your keyring (or other equipment) and help protect it from accidental loss. WaterBuoy offers the following features...
Able to lift up to 1kg in weight
Reacts in seconds to contact with water
Keeps on floating for up to 24 hours
Powerful built in flashing high intensity LED light is visible at night and up to 250 meters
Weighs a mere 32 grams and is very compact at just 7cm in length