Being prepared for an emergency communication assignment involves a wide range of considerations: radio equipment, tools, power sources, along with clothing, personal gear, food and water.
Having a go-kit planned and assembled ahead of time raises your level of preparedness, allowing for a quicker response when that call-out happens. Your kit should be tailored to your needs, your typical assignment and for a typical duration.
In addition to items usually on your person at all times, such as photo ID, cash and coins, cell phone and watch, a very basic go-kit consists of a handheld radio, extra batteries and a portable charging system to keep you on the air for the duration of the event, contained in a convenient to store and carry bag.
An online resources I found suggested a few additional items should be readily available in your go-kit, such as:
A copy of your current amateur license
Speaker microphone
High gain HT antenna
Antenna adapter - SMA to SO-239, as an example
Flashlight and spare batteries
Pen or pencils and paper
ICS and Radiogram forms
Multi-Tool or Pocket Knife
ANSI Type II Reflective Vest
Water
Small Bag of Snacks
First Aid Kit
Group or organization credentials
For extended events of 24 or more hours additional clothing and personal care items are suggested.
Ideally, you should divide your Go-Kit into small, easily-transportable modules, based on expected type of assignment, length of assignment, and storage location. An event lasting a few hours will not require a bag of clothing and personal care items, but Go-Kit modules should supplement each other with additional equipment and supplies, to extend your capabilities and endurance.
If you are interested in assembling a go-kit I encourage you to search amateur radio go-kit on the web.