They will love any big pieces of fallen branches from the woods - pine etc, as the underneath will be full of bugs for them to peck at.
They do love to scratch so sand, grit and bark chiooings in different areas are great for them, I use the large water trays from the greenhouse that you stand seed pots in as baths, I fill one with water and one with a mix of sand/oyster shell for them to bathe in and pack at.
They also love tomatoes, apples and cornflakes or bran flakes as treats on top of their normal food, and a bit of straw or hay that they can nest in, in a sheltered area, under a bush or tree makes a great den.
Water bowls or drinkers in various spots gives them a walk out to stretch their legs and have a nosey around, and I am sure if you put a tray of dying seedlings or plants in there that you are not bothered about the slugs will go in there and give them some extra protein as well.
Mine are all free range now, and these are the sort of things they go after. Hope it helps to give you some ideas.
Julie