Assuming the UUID of the USB stick's file system is 866E-E1E1
UUID=866E-E1E1 /mnt/disk vfat rw,nosuid,nodev,uid=Basso,gid=Basso,dmask=0077,fmask=0177,utf8=1,noauto,flush,noatime 0 0
I assumed Basso is your default group for gid=. nosuid and nodev are for security on mass storage devices. Consider no exec option as well. No auto is needed to prevent booting failure is the USB stick isn't plugged in. You could use nofail instead. The 'owner's option will let you mount the pen drive without needing to use sudo.
With these permissions, only user Basso can read files on the pen drive on that computer.
I used the uuid number, so it will boot even if a different device node is used the next time.