Barcode scanner
Barcode scanner devices exist in many forms, some of which are quite cheap, and others of which are quite small and portable. The smallest are infrared contact devices, similar to those used in checkout counters, worn on a ring. All of them read barcodes.
The mobile device code to integrate these with another body-worn device, communications networks and the rest of the healthy buying infrastructure will typically have to run on Symbian or another mobile OS. Python support for these devices is the most likely integration path.