PSoC3 can act as a USB Full Speed Device but not as a USB Host. So, storing data onto a flash drive using USB protocol is not supported, but there are examplpe projects available which have been used to interface with the micro SD memory Cards.
Let us know if it would be helpful.
Can it be possible to share example for interfacing psoc3 to micro SD card?
Not a good idea hijacking a 5 year old answered thread for a quite different question.
Nonetheless_: Welcome in the forum.
Hardware interface to micro SD is SPI which PSoC3 can handle easily. You will need the emFile library from which I do not know exactly whether it runs on a PSoC3 (8051 core), but it should...