You can also take some of your crumble feed and spread it like scratch feed in the spot you want to take them out in. Just don't expect them to get to far from the coop or venture to much their first few times out. They are just learning as are you.
Enjoy your field trip. And keep us posted.
Most crumble or pellet feed has some grit in the mix.
I free range my flock and I have never worried about it. Start them out at about an hour or so and go from there.