Is it permissible to use meal vouchers to purchase other food items like milk and sugar instead of prepared meals?

If the questioner bought the tickets, selling them is impermissible; because it falls under the sale of Salam (forward sale) before taking possession. The ticket is like food that is a liability on the seller, and selling it before taking possession is prohibited. However, if the tickets were a gift, then those who say that a gift is owned by the contract permitted its sale and disposal, while those who say that it is not owned except by taking possession prohibited its sale before taking possession.