The optimum conditions for storage of chemicals is cold, dry, dark and oxygen-free.
The more of these criteria you can meet, the better. It's recommend to store your chemicals in a sealed container inside a freezer. Stored in this way, drugs will outlive you.
Worth noting though, if you remove drugs from the container while still cold, they will attract condensation, which is to be avoided. The best way to avoid this is to leave them in the sealed container until they reach room temperature.