A trick I worked out in my bachelor days (alright, I still do it occasionally): if you have some food that is in the gray area (figuratively, not visually) of bacteria growth, mix some alchohol in with it before you reheat it. If it turns visibly lighter in color (like, white flakes appear and float to the top of the alcohol) when the alcohol hits it, it's got significant bacterial buildup and should be thrown out. If you can't see any visible change, it's either still good, or you can rely on mixing enough alcohol in to kill anything bad.
This works best of soft foods, as getting the alcohol to the inside of solid foods can be difficult (but not impossible). Soup, chili, and pasta are ideal candidates. Reheating the food to a high temperature also aids in killing bacteria. Foods that are more likely to cause horridness when they go bad (like seafood and mayonaise) are not ideal candidates.
The above method is not sound medical or legal advise and should not be followed by anyone except in cases of potential starvation. Neither myself nor Enworld is responsible for any negative effects caused by performing this test. Please drink (and eat alcoholic foods) resposibly. Never drink and drive. Do not use alcohol if local law prohibits it for any reason. Do not perform this test while sleeping. For best results, squeeze from the bottom of the tube. Rinse and repeat.
