Its just impossible to connect a USB flash drive to a PIC18F4550 controller. (You need a controller with USB HOST, Example PIC controllers are PIC24 and PIC32 series)
k, if your using a PIC32 :? again there is problem, you can't connect two USB drives(Flash drive and bluetooth dongle). Microchip USB Host/Device stack is free, you can download it from their site. Anyway go ahead post your doubts here.
Check this this video (PIC32 reading text file from a 4GB flash drive).
Good Luck.