If you’d asked this 20 years ago, it would have been a library and a notebook. Today? A good laptop or tablet. You can store the rule books, have a dice program, notes, maps, pictures, mood music — whatever you need. Need to access information on the fly? If you’ve got wifi, there you go.

When I was running Battlestar Galactica, I used my MacBook Air because I would have so many windows open to access character writeups, ships, etc… Running Hollow Earth Expedition, I often just use my iPad or laptop. For the current D&D game, there’s such good support apps — I highly recommend Game Master 5 and Fight Club 5 — that I use the iPad exclusively.