Handling registration of multiple participants for an event?
This by default is not available in CiviCRM ATM. You can alter the message template under System workflow message for 'Events - Registration Confirmation and Receipt (off-line)' to include additional details. If you are good in smarty variables than you can use api to fetch details like additional participant or payments and include it in your message template, or you can create extension to 
 implement tokens and tokenvalue hook to add tokens and process the value when rendering message template before it is send to user.