At some events it may be useful to create an ad-hoc Wi-Fi network. An ad-hoc network is an isolated network, and it is usually created by a computer or similar device, rather than by a Wi-Fi router. You can think of it as a Hotspot without an Internet connection.
At a later time I will summarize the steps in a way that doesn’t plagiarize the original content, and we will also pre-configure the MASTboot image to be able to start an ad-hoc network. Until that time, you should be able to follow the instructions here: http://www.ubuntugeek.com/creating-an-adhoc-host-with-ubuntu.html
Be aware that bandwidth for Wi-Fi is limited. Be careful in assigning channels to your ad-hoc networks, so that there is not much conflict between the channels. Keuwlsoft Wifi Analyser app for Android is a handy visual tool for seeing what bands are in use in your area.