Watch out. That is the best advice I can offer. Everything is going along well and then all of a sudden the screaming starts. Toys or other items nearby are getting thrown. And it is too late. Your child has hit the wall. All you can do is try to get them to the nearest car seat, stroller or crib for a nap. And then hope it works. If our son goes too far past his point, he will not rest and his level of difficulty will reach maximum proportions.
This can all be prevented if you know your child and keep him or her on a schedule. I have said it before and I will say it again (and again and again) - our children need sleep. End of story. No shopping, dinner, game, etc. is more important than your child's sleep. If they get enough sleep they will be happy and healthy. If they do not, then they turn into the devil child and wreak havoc on everything in their path.
When you plan your day, account for nap time. Do not take your child out for lunch at 1 if they sleep from 1-3. It is common sense (which is not so common). Let them sleep and do not wake them. Please oh please do not wake them. If you allow your child's nap and sleep schedule to dictate your activities, everyone will be the better for it. Trust me.