First, use lsblk
to list your block devices. Note the path containing your usb device. e.g. /dev/sdb1
Next mount the device to an existing folder or create a new one.
mkdir -p /mnt/thumbstick
mount /dev/sdb1 /mnt/thumbstick
Now you can pipe the dpkg output to the usb device.
dpkg -l > /mnt/thumbstick/packages.txt
Finally, you can unmount the stick to ensure everything is flushed. (optional)
umount /mnt/thumbstick
So basically r/lounge?