I was approached a few years back about this problem for a restaurant.  They wanted to outfit everything with sensors everywhere and a new point-of-sale(pos) that also integrated inventory control systems.  Their PoS would display items as available when they really weren't.  We did integrate a punch of RaspberryPi devices outfitted with all the sensors they wanted, not just needed.  Everything was streamlined and even added a few thermal printers to tag items as they came in to maintain the FiFo and reduce the back stock they had.  Instead of centralized ordering kiosks, every employee got an iPod because trendy.  They were able to recoup costs by the reduced food waste, and schedule employees better too.

Sadly before the project could move into its next phase I moved far enough away to not be an active member.  They were going to add sensors to the kegs to weigh them when they came in to measure just how much was left and display it above the bar.