The most useful communication method?

There are zombies all around. If they get even a hint that you're here you can kiss your arse goodbye. You need to tell your companion where to go, what to look for, and to get the keys to the car parked out front. What do you do?

You sign. Sign language is a fantastic thing to know (I see Obama is in the news again for his signing skills) and VERY useful if you need to keep quiet. A lot of signs are self explanatory and it wouldn take long to teach a companion the essentials. After a while you would be able to "talk" in your downtime without fear of attracting attention!

Something else to remember: we are the most prepared. If any of us want to travel with others we will have to become teacher and pass on our knowledge and skills!