Communication is a vital key to keeping a group together. It has been integrated into war since war itself was waged. Communication is vital to movement of troops as well as retaining situation awareness in combat and other situations. Maintaining good communications after disaster will prove to be very proactive in saving lives, and staying prepared for coming events in any prepping scenario. Although some scenarios might prevent effective communication between individuals and groups after disaster such as an Electromagnetic Pulse attack, there are several alternatives that have been in use since the beginning of war that you can utilize to keep your group together.
Obviously, the best solution is to have a radio set. Depending on the size of you group, you may have 3 radios, or up to 10. In the case that your group is around 30 or more, having about 3-5 radios connected to each other will be your best option, having your group of 30 split into 3 squads of 10 and giving one radio to each squad leader is the best option. Not only will this improve the quality of information being transferred, but it will reduce the cost of resources needed if say, every single member had a radio. Giving the squad leader this option will improve the overall cohesion with the rest of the unit, give outstanding situational awareness as to what is happening with the rest of the groups, and give each squad leader the capability to conduct movements in correlation to the other squads movements,positions, and operations.
Some cheap options are available for some walkie talkies , how ever it is recommended that if you have the funds, you purchase military grade communication devices that will transmit signals for miles and ensure that your units are never cut off. There are some limitations to these devices how ever. If there is an electromagnetic pulse attack, all communications will go down, electrical devices will stop working rendering your devices useless. This is where old age technology will have to come into play. Going back to ancient warfare, armies used horsed runners who would deliver messages from riding their horse between groups and delivering orders or information. This can still be used today is an electromagnetic pulse attack occurred. Another option is to look at the tactics of the native Americans. They used smoke signals using fires and blankets to make short signals of smoke by blocking the wave of smoke momentarily using their blankets. This is also effective as well as the use of signaling mirrors. Using Morse’s code, you can send out signals with a mirror to other members of your group or to any other individuals you see fit.
These methods of course were used in the great plains by Native Americans and will not be as affective when used in dense forests or jungle like vegetation. When these climates are prevalent other methods will be needed such as making certain vocal noises or uses instruments such as whistles or wood devices to inform of positions or enemy movements. This technique was used to a devastating effect in Vietnam. Enemy soldiers would hide in trees and tap on the wood to inform their comrades of US and allied positions.