5E DM Screen
The Official Screen
There are lots of great materials printed on the official Dungeon Master's Screen Reincarnated made by Wizards in 2017. This dungeon screen is four boards long and is made from durable cardboard. It is a shiny lamination to keep it protected from basic spills and usage. One side has the dragon artwork created by Tyler Jacobson.
Over the middle of the folds is the conditions and then each of the sides have information as stated below.
This side has the basic actions that can be taken in combat such as attack, dash, disengage, help and ready to name a few.
There is a brief list titled "Things You Can Do on Your Turn" along with explanations on jumps, suffocating and concentration.
The right side talks about stations of exhaustion. There is a great deal of DM references such as: setting a DC, tracking a DC, damage by level and severity, object hit points, object armor class, skills & associated abilities, travel pace, services & costs along with the costs of food/drink/lodging, obscured area rules, encounter distances, cover and effects and lights.
DM Wolfsfox's Additions
There are other things that I have in addition to the standard print that I use in reference during my games that have a home on and behind my DM screen.
I got these cards from Gyld and I use them to keep track of initiative when we have in person gaming and use them to keep track of player AC, max HP and their passive perceptions. I like that I have the AC's so I don't have to ask every round if something hits a player or not.
Xanathar's Guide Encounters
I love the random encounter tables that are sorted by location and levels that are provided by Xanathar's Guide. I usually have either a printed version of what area/level is appropriate for the group or create my own post-it version to refer to during travel and other PC explorations.
Something that is important to the game but rarely used is the weather. I try to have 2-3 things written for the weather before we go into the game. Is it a full moon? Will there bee any cool astronomical events in the evening? Temperature, precipitation, wind and other weather related items can impact travel and can be used to add details to your game. I usually jot down a few ideas that can be used. It does not have to be fancy and sometimes they just go in the folder for next session. If you do not want to pre-create a list you can also use Donjon to find a random weather generator.
Things I Needed to Research in the Past
I also keep handy a list of rulings that I have made in the past and notes that I had to look up. Some of these things include:
tossing rules (like players tossing players)
AC and hit points of walls (think koolaid man)
Polymorphed creatures vs shear cliffs
How far can I yeet an octopus?
Can I use Crack to take down this tower?
Can I use Darren's Instant Fortress to shish kabob the Kraken from the inside?
How much smoke does it take to kill someone from smoke inhalation?
Some of these things have lead to some crazy and interesting rp and combat moments.