In the interest of OPSEC, the use of a One Time Pad (also called a cipher) to encrypt your communications with others in your group is, IMO, a no-brainer.
What is a One Time Pad? Start here
One Time Pad from wikipediaMore information than you need to know:
http://users.telenet.be/d.rijmenants/en/onetimepad.htmI see this as a tool used when you need to send a message (written) to someone and you cannot trust that the message will not be seen by other than the intended recipient. Read between the lines, please...
For example, say that you need to leave a message at your location about where you are going (ie, you are "bugging-out"). The message might state your destination and perhaps instructions on how to follow, or to NOT follow you. This is information which might be life threatening in the wrong hands (think gangs of looters working the evacuated neighborhood...).
This product (commercial, it costs money, less than $10), is a quick means of encoding and decoding messages.
http://prudentsupply.com/?page_id=417Let me state that this tool is NOT strictly necessary, since you can make a coding pad using only a pen and paper, BUT that takes time. This tool has the advantage of speed, which may be important, depending on the situation...
The article gives a good, detailed explanation of use, with pictures.
I DO advise that you practice using One Time Pads, creating them by hand using pen and paper. This will give you the necessary understanding of the coding/decoding process. Then you will appreciate the benefit of using this quick tool.
Finally, the One Time Pad requires that both sender and recipient have the key (which is NOT this tool). Without the key, the message cannot be encoded or decoded.