Whenever my group plays a game, I like to see if anything happened on that date that I can reference in the game session.
Most of these are nodded at by simply referencing the event that happened on that date in game.
Whenever I didn’t know the actual date something was published, I would get it by averaging the year it was published in.
I also shifted ‘the empire strikes back’ and ‘return of the jedi’ days a month ahead and to the beginning of the correct month, to avoid overlap.
The thirteenth day of each month is also associated with a specific in-game tragedy, which is used as much as sensible in games held on the thirteenth.
On Birthdays, everyone gets in-game presents! each month also has a day for one of the od&d classes, and one for a d&d monster. Personally I choose to honor those days at least once, even if we don’t actually play on them.
JAN
1 ADOM 1.1.1 day
2 Fighting Man day (Fighting classes gain in-game rewards, usually inconsequential or strictly novel, e.g. romance, novelty magic items, a bardic poem dedicated to them)
3 J.R.R. Tolkien’s Birthday (presents can include: mithril mail, magic black arrow, rings, broken magic sword, treasure map (with moon runes)
13 Trap day (traps!)
22 Robert E Howard’s Birthday (treasure, weapons, treasure. elephant idol with a jewel for a heart. magicians get half treasure.)
31 Displacer beast day
FEB
1 ‘Call of Cthulhu’ day
2 ‘Call of Cthulhu’ (RPG) day (call of cthulhu tribute, plus sanity mechanic)
3 Magic User day (fighting man day for Arcane magician classes)
13 Item Destruction day (monsters use a lot of sunder attempts. spellcasters really like shatter. throw in some item-destroying traps. don’t overdo it, though.)
28 Bugbear day
MAR
1 Cleric day (see previous class days)
4 Gary Gygax deathday (exactly one character must die horribly during this session. don’t let players know who has been chosen, just let their doom hang over their heads)
9 my group’s anniversary! ‘Henry V’ day
13 Curse day (curses!)
14 Temple of Elemental Evil day (play ToEEesque adventure if at all possible)
15 H.P. Lovecraft’s deathday (use sanity for this session. do your best to drive characters insane. at least one character must die VERY horribly.)
31 beholder day
APR
1 ‘Nodwick’ day
2 Dwarf day (meaning the class, but the race also gets rewards if you aren’t using race-as-class)
7 Dave Arneson’s deathday (at least one player should be killed by monks and/or assassins.)
9 ‘Macbeth’ day
13 Disease day (DISEASE)
16 Ravenloft day (play Ravenloft tribute adventure)
23 William Shakespeare’s deathday (flip a coin. if heads, tragedy. do your best. may take multiple sessions to complete. if tails, comedy. everyone gets a romantic interest.)
26 William Shakespeare’s baptism date (his actual birthday is unknown. presents include daggers, crowns, etc. try to fit in either a ghost or a doppelganger.)
28 Terry Pratchett’s birthday (presents include invisible hats, pearwood objects, large gold coins, animated books, lilacs.)
30 Mimic day
MAY
1 ‘Return of the Jedi’ day
2 Elf day (see Dwarf day.)
4 ‘Rogue’ day (the computer game, not the class. the thief class is later on.)
13 Deadly Poison day (con damage, gotta love it.)
14 ‘Conan the Barbarian’ released in the US (NPCs suddenly think the characters are totally cheesy for a session.)
16 ‘Attack of the Clones’ released (if any of your characters has a backstory with any room to fit crap in, do so. have them come face to face with an annoying friend from their new craptacular backstory. remove this embarassing past after the session, to be merciful.)
19 ‘The Phantom Menace’ released (see the 16th.)
20 ‘Revenge of the Sith’ day (see the 16th.)
25 ‘Star Wars’ day
31 Owlbear day
JUN
1 ADOM 1.0.0 day
2 ‘Hamlet’ day
3 Halfling day (see Elf day and Dwarf day)
4 ‘Star Trek: Wrath of Khan’ day
6 D&D 4e day (try to kill off any characters that wouldn’t fit in with the new edition (gnomes, half-orcs, improperly aligned, spellcasters who know ‘wish’,))
11 Robert E Howard’s suicide (1 character must die. spellcasters exempt.)
13 Permanent Ability Score Damage day (you choose which die size to use)
21 ‘The Empire Strikes Back’ day
30 Blink dog day
JUL
1 Thief day
3 ‘T2’ day
13 Negative Level day (achieve using level-draining monsters)
27 Gary Gygax’s Birthday (gifts include spellbooks, maps to gygaxian dungeons, guns)
29 ‘The Fellowship of the Ring’ day
31 Couerl day
AUG
1 Solomon Kane day
2 Monk day
13 Highly Malevolent Magic item day (bags of devouring, swords of berserking, you name it.)
15 ‘Star Wars: The Clone Wars’ day (see the prequels)
20 H.P. Lovecraft’s birthday (gifts include small figurines of monstrous figures)
22 Fafhrd and The Gray Mouser day
31 Gelatinous cube day
SEP
1 Tomb of Horrors day (tomb of horrors style adventure. you can choose to give people temporary characters so that they don’t kill off their main ones.)
2 Assassin day
5 Fritz Lieber deathday (all swords owned by party members shatter at once)
13 Wish-Gone-Wrong day (give them a free wish, then mess it up)
21 ‘The Hobbit’ published
29 ‘Order of the Stick’ launchday
30 Flail snail day
OCT
1 Dave Arneson’s birthday (gifts include spellbooks, boardgames, figurines)
2 Antipaladin day (if you have any in your party. if not, just have them battle antipaladin NPC)
5 ‘The Colour of Magic’ day
13 Inappropriate Encounter Level day (my personal favorite)
20 ‘The Return of The King’ day
26 ‘Terminator’ day
30 Vargouille day
NOV
1 Paladin day
11 ‘The Two Towers’ day
13 Random Divine Smiting day (yes!)
30 Flumph day
DEC
1 Conan day
2 Druid day
5 Paranoia XP day (everyone gets six lives. player who dies least gets valuable magic item.)
13 Natural 1 day (each time someone rolls a die, flip a coin as well. if tails, discard the actual die roll and replace with a natural 1. flip once for groups of dice. [2d6 would have one coin flip, and would count as ‘2’ if tails])
24 Fritz Lieber’s birthday (swords. swords for everyone.)
31 Tarrasque day
I also enjoy Actual Holiday-based effects, like letting everyone play monstrous characters for one session on halloween, or merging with 1000 Blank White Cards for April fools.
Reign of jotuns 