You need to minimize the amount of thermal energy that moves into the drink from the warmer air around it. Putting it in a thermos or vacuum-insulated tumbler is one way to do this. The lack of air between the two layers of the container slows down the transfer of thermal energy. Another way to do this is to surround your cup with a material that has a lot of air space in it, such as cardboard or foam. The air space slows down the movement of thermal energy.