My wife and I did a similar theme a few years ago. In short, we were Steampunk Ghostbusters, though none of our equipment or uniforms were really modeled off the original Ghostbusters.
Some sort of detector or meter would be appropriate. I made one out of the plastic frame of an old receipt printer, some analog car gauges, and some green toy test tubes. It fit over the hand kind of like a gauntlet. I'll see if I have photos of it somewhere at home... we didn't carry it around too much because it was a bit bulky and heavy.
A name badge on your shirt, and some calling cards.
A bandolier with your hunting apparatus, chemicals, etc. Some toy test tubes with some harmless liquids inside (e.g. corn syrup and food coloring), with aged-looking labels.