Hi,
There are USB_Hosts, one in a system, providing power, controlling the bus, controlling the timing. (Like a PC)
And there are USB_devices. Slaves somehow, there may be many in one system. (Mouse, hubs, keyboard, printers, USB_sticks, canera, audio device..)
A quick internet search showed that your PIC can only act as USB_device, but to communicate with an USB_memory_stick you need your PIC to act as a USB_host.
I have no experience with PIC, but on first sight it seems that your idea is not possible to do with this PIC.
Klaus