I always go by the 4-40-140 rule. That means that no food should be between 40° and 140° (thanks for the tip, dullard

) for more than 4 hours. i.e. If you leave leftovers in your car while you go to the movies on a >38° day (food is 2° warmer than the surrounding temperature), the leftovers need to be thrown out. Your food dropped below 140° at the restaurant and won't reach 40° until after being in the fridge for at least 30 minutes. Unless you watch a short movie, get there right when it starts, and have a short drive home, then your food will be in the danger zone for more than 4 hours.
Some are more strict and use a 2-40-140 rule only allowing 2 hours in the danger zone, but I think that goes a bit too far. If that were the case, then you could never use a slow cooker.