i'm not sure about vegs, i think most of them might be unsafe because they can cause gas, but someone else will hopefully answer that.
i can tell you some other safe treats:
unfrosted cheerios, unfrosted shredded wheat, old fashioned oats [not the instant], rosehips, rose buds, chamomile, peppermint, oregano, thyme, hibiscus, red clover just to name a few.