Is it permissible to keep soft drink cans in excess of one's need to barter them for goods, knowing that these meals are deducted from one's salary?

If meals are deducted from an employee's salary, they become his property to dispose of as he wishes without the company's permission, because a condition that contradicts the intent is void. Therefore, he is permitted to keep the containers or exchange them. However, if the institution pays for the meals and does not deduct their cost from the employee, then he is not allowed to dispose of them except according to the institution's conditions, as the Prophet, peace and blessings be upon him, said: "Muslims are bound by their conditions."