What exactly are you trying to achieve? Do you want to have access to a mass storage device as Fran.B suggested? If so, this other link is also helpful: Re: detect USB drive on intel edison
I believe it is simpler to create a service that mounts the flash drive on boot. It is quite simple and should not take that much time. You will need two files, the first one is a shell script that we'll call mount_flash_drive_on_boot.sh and, for the sake of this example, it will be stored in /home/root/:
#!/bin/sh #Create the directory in case it doesn't exist, if the directory exists the command will be skipped by default mkdir /media/fhdr #Mount the flash drive if it exists, if it doesn't skip this command. mount /dev/sda1 /media/fhdr
Once you've created this file in your Edison, make it executable with:
chmod +x mount_flash_drive_on_boot.sh
Now we need to create the service that will start the script on boot. The service can be called however you like but it must have the extension .service. In this example it will be called mount_flash_drive_on_boot.service. All services must be stored in /lib/systemd/system/:
#!/bin/sh [Unit] Description=Service that mounts a flash drive connected to Edison on boot to the directory found in /dev/fhdr [Service] ExecStart=/home/root/mount_flash_drive_on_boot.sh Type=idle [Install] WantedBy=basic.target
Once you've created this file you can enable it with the command:
systemctl enable mount_flash_drive_on_boot.sh
After this is done you should be able to see that your flash drive is detected and mounted on boot (if it is connected of course).
I understand, in that case, you can take this recipe as an example: https://git.yoctoproject.org/cgit/cgit.cgi/meta-intel-edison/tree/meta-intel-edison-distro/recipes-support/blink-led.
As you can see in it, what it does is "install" a service that blinks the Edison's LED. But as you may know, a service is not the same as a package, it does not need to be installed, it just needs a couple of files to be stored correctly. In the recipe you can find the directory called files, there you will see precisely the service files called blink-led and blink-led.service.
Now, if you read the content of blink-led_0.1.bb, you can see that the recipe is, again, "installing" the files and the specific location where they will be stored.
In case of blink-led, it will be stored in /bin/ and in case of blink-led.service, it will be stored in /lib/systemd/system/. So, I'd suggest you to take this recipe as an example to take your files and store them in your custom image.
Recipe for oobie (Re: Disabling default edison web server while creating the image) may be better example here. As it is directly using cp -r to copy the whole directory instead of individual files.