Simplify the following text for a Grade 4 native English-speaking person.
Original: A first aid kit is a collection of supplies and equipment for use in giving first aid , and can put together for the purpose ( by an individual or organization , for instance ) , or purchased complete . There is a wide variation in the contents of first aid kits based on the knowledge and experience of those putting it together , the differing first aid requirements of the area where it may be used , and variations in legislation or regulation in a given area .
Simplified: First Aid kits are used to perform first aid on injured people .