What is the value of a meal voucher included in employee's gross income?

CJ Hospital maintains a cafeteria on its premises. In addition, it rents space to Subway, a privately-owned sandwich shop. The cafeteria closes at 8:00 pm. Subway is open 24 hours. Charlie provides meal vouchers to each of his 240 medical employees to enable them to remain on call in case of emergency. The vouchers are redeemable either at the cafeteria or at Subway. Although the employees are not required to remain on or near the premises during meal hours, they generally do. Charlie, CJ's Chief Administrator, has approached you.