Bike lights, to be precise. I've never been bothered about riding in the dark, probably because I learnt to drive in the winter and therefore mostly in the dark. The basic, regulation, one white, one red would be enough. Nothing fancy, just what you need to stay within the law and drivers' eyesight.
But then a pothole shook the rear light loose, and its red cover smashed. Only after I'd bought a replacement did I realise that the bulbs still showed red, as long as I held the batteries in with some clingfilm and sellotape: so now I had a spare to clip on to the back of my collar as a supplement.
Then I bought my Winkku, which also has front and rear lights. So now I could have one red light showing to one side as well as the original on my collar and the replacement on the saddle post.
And then my rear reflector cracked and fell off, and the only replacement I could find that fitted and helped hold the rear mudguard in place was yet another light with all sorts of sparkling and flashing options. How could I resist?
I'm almost a one-man mobile red light district.
But that was before I saw these: