Keep your powder dry until you need it.

Meaning

- Be prepared and save your resources until they are needed.

- If you keep your powder dry, you act cautiously so as not to damage your chances.

- The trick of sending a copy letter to the CEO - and showing this on the letter to the customer services department - is likely to have the same effect. Keep your powder dry until you need it.

Origin

The allusion is to gunpowder which soldiers had to keep dry in order to be ready to fight when required.

by the way...

guns? no thanks!