From my chemical-free yard:
Dandelions (leaves and flowers)
Clover (leaves and flowers)
Wild violet (leaves only)
Henbit (not real wild about this)
Wild strawberry (mainly leaves)
Plantain (yard weed)
From the grocery (fresh only): Collard greens, mustard greens, kale, endive, pre-packaged salad mix (only clean leftovers from my meals - this is too expensive for regular feeding), squash & carrots (limited amounts).
Cactus pads when I can find it.
Pretty Pets tortoise pellets - they like it dry but I also mix it with soaked Timothy Hay. I'm going to try Alalfa Hay next.
Also Hibiscus flowers.
I add Repcal calcium&D3 to the weeds/greens/vegetables, but not to the pellet/hay mix. I also leave them some cuttlebone to gnaw on.