Best Design for Under A Tenner?

I’m sure this will be all over the place, a vote on what was the best piece of design you can get for under a tenner. Full of fun stuff:

The condom dates back to ancient Egypt but is named after Charles II's physician, the Earl of Condom, who developed a 17th century version to protect the king from syphilis. They have been rubber since the 1840s. The paper clip was invented in 1899 by the Norwegian scientist Johan Vaaler although a British company, Gem, developed the double oval shape. The Underground map was designed by Harry Beck in 1933 and its format was based on an electrical circuit.

The winners were:
Laszlo Biro's 1930s invention - a long-lasting pen with quick-drying ink . The remainder of the public's top five was the paper clip, the London Underground map, the condom and Velcro.

There is another point that can be drawn from this list, that is the power of mass manufacturing, that thing that capitalism does so well. Two of these, when first introduced, cost way way more than 10 pounds each in current money. The Biro and the condom. It is design mixed with that mass manufacturing that makes them so useful, not the design on its own.