Aero Scale

By using the barometer sensor in your phone, and a reference weight (default a pre-2012 Canadian $2 coin), you can, with the aid of a sealable bag, turn your phone into a scale.

Place your phone in a bag, inflate, and seal it. Lie it flat to trigger initial zero-weight calibration. When it asks, apply the reference coin weight and wait for the coin-weight calibration. After that is complete, you can (carefully) measure weights. Do be careful as the weights are over your phone!

Note: The resulting values may be precise, but their accuracy will be poor. Either from miscalibration, leaks in the bag, or structural changes in the bag. For the best result use a soft bag.