If you're looking for the lightest bike pump ever invented, it's the iPump Micro from a little known company in Japan called Morris Ostrow, which “championed the spirit of interesting and useful, cutting edge, quality designed products in Japan for over 30 years”. At 21 grams, the iPump Micro features a carbon fibre exterior to maximize air chamber capacity without sacrificing strength and stored inside the pump is a sliding nylon hose to make it easier to connect to awkwardly placed tyre valves. It's so small it fits inside your bike seat post and its recent successful Kickstarter campaign may have proven its appeal. However, its small size may mean that it'll take longer to inflate a tyre compared to standard pumps. In case of emergencies, that's better than having no pump at all. However, you might first want to consider something like the Topeak Road Morph G Bike Pump. It may not be hidden like the iPump but it pumps better and can be mounted on your bike.
More at iPump.jp