If you are not required to take a friend and the mystery shopping company is not furnishing a reimbursement for the friends' meal, I believe that is your personal expense and you cannot deduct it.
With groceries, unless you cannot make the required purchases within the reimbursed amount you cannot deduct the overage. For example, you have to buy one item from pharmacy, one item from deli, and one item from bakery, and you are reimbursed X dollars. You cannot deduct the overage UNLESS you purchase the least expensive item in each department and the total is still more than the reimbursement.
This is just my opinion, I am not a CPA or an Enrolled Agent.
Mary Davis Nowell. Based close to Fort Worth. Shopping Interstate 20 east and west, Interstate 35 north and south.