I suggest obtaining the name and address from reservations for the Station Manager of the airport you were delayed in.
Depending upon the time of day you were scheduled to travel and if any meal had been planned for your flight, and the length of your flight, it's generally assumed that you never planned on UA providing you with a meal in the first place. If the decision was made to have dinner provided onboard rather than write vouchers for everyone to use at the airport,this should have been announced and also explained thoroughly to customers requesting a meal voucher.

At the very least, a written response from the Station Manager will assist you and your friend in obtaining any mileage compensation from HQ by enclosing a copy.