The easiest way to hide files on both Windows and Mac is by using a Windows Computer if you have one spare. On Windows using supported file systems, files can have a hidden flag that is set using a check box under the file's properties. A Mac will acknowledge this flag and hide the file as well. If you have a spare Windows computer and the files are on a Windows compatible flash drive (FAT32 etc.) you can right click on a file and open it's 'Properties', on the 'General' tab there is a check box marked 'Hidden' that you can check.
This same functionality can be achieved on a Mac as well but using the Terminal instead. To do so navigate to a file that is on a FAT32 formatted drive (MS-FAT in Disk utility) using the cd command (for example a drive that is called PENDRIVE would require the command cd "/Volumes/PENDRIVE" with or without the quotes, using quotes is recommended for path names with spaces in them) then use the command chflags hidden followed by the file name in quotes (e.g. chflags hidden "./MP3 with spaces.mp3") Look here for more details:
http://osxdaily.com/2012/07/19/hide-file-mac-os-x-chflags/