Attach Bacteria Cultures to Packages of Food

To take the guess work out of detecting food spoilage, one could attach miniature bacteria cultures to each container. A culture would consist of a sample of the product which has had a little more time and opportunity to spoil than the rest of the product in the package. It would be tightly sealed in a clear plastic packet about the size of a single-serve packet of catsup. The sample would also contain the right amount of oxygen and nutrients for the bacteria expected to cause spoilage. Since each culture would be exposed to almost the exact same conditions as the package of product it's attached to, its growth would be a suitable predictor for that of bacteria in the product.
The consumer would check the culture for visible signs of spoilage and use that to judge the safety of eating the product. If a sample looks bad, then the product itself is also well on its way to spoiling and should therefore be discarded. On the other hand, if a culture having more time to spoil than the product shows no sign of spoilage, then the product should be fine also. One should always check the product for signs of spoilage though, just to be safe.

Note that this idea does not suggest adding bacteria to the samples. There are already bacteria in any normally prepared food. The best we can do is reduce their rate of growth.