My previous post told you what was in the original edition Dungeons & Dragons boxed set. But, what wasn't in the box? There were some surprising omissions from the set, as well as non-included items that are only notable in retrospect.
Dice: polyhedral dice were not impossible to find in the mid-70's but they weren't easy to obtain. Folks at TSR and elsewhere caught on to this fairly quickly but of all things not in the box this seems the most glaring oversight.
Chainmail: cited in the rules as a method of resolving combat. Indeed, the rules refer to the combat system actually included as the Alternate Combat System. Not quite as surprising a lack since few folks actually used Chainmail for running D&D except when resolving mass battle scenarios. Gary Gygax, one of the co-authors of D&D, also co-wrote Chainmail and even he didn't use it for resolving one-on-one combat.
Outdoor Survival: a product by another company: The Avalon Hill Game Company. Outdoor Survival's rules and game board formed the backbone of the wilderness (non-dungeon) based adventures in D&D. As with Chainmail, most of what you really needed to know was repeated in the rulebooks, but the playing board was very useful for "lost in the wilderness" scenarios.
Adventure Module: not as surprising a lack. The lack of a module is more notable from looking back at years of introductory boxed sets that did include a starter adventure.
Thieves: now a staple of D&D, this fellow was notably absent from the original rules. The thief didn't appear in official rules until Supplement I: Greyhawk was published a short time later. When asked by a newer player how we opened doors (etc.) without thieves the referee in me came out and replied, "How would you do it?" For the record, a lot of doors got bashed in, a lot of chests were pried open with a crowbar.
How To Run Elves: the rules implied the elf was played as two distinct characters, a fighter and magic-user. Depending upon which he was playing as during an adventure the elf would have abilities he might not have when playing as the other. An elf magic-user couldn't wear armor or wield a sword, an elf fighter couldn't cast spells or use certain magic items [on a side note, co-author Gary Gygax confirmed this interpretation was how he intended the elf player-character to be played]. So, how do you figure "to hit" in combat, saving throws, or hit points? Was a 4th Level Fighter/2nd Level Magic-User a 4th level character of a 6th level character? Later editions of the game would hand-wave all this away and meld the 2 classes into a hybrid F/MU class many folks found more palatable. I felt, and still do, the original way of running the elf makes them feel more unearthly and fey, preferring it to the more modern interpretation.
Any Sub-Class: sub-classes or variant classes of any kind. Paladins were the first sub-class and were introduced along with the thief class in Supplement I: Greyhawk. The ranger and the illusionist appeared in the pages of TSR house organ The Strategic Review. Druids and monks appeared in subsequent rules supplements.
Magical Armor: by implication was limited to maximum bonus of +3 and only for plate.
Magic Swords: increased chances "to hit" but didn't always grant bonuses to rolled damage.
Monsters: many not included in the boxed set would later be considered rather iconic to D&D such as Beholders, Bugbears, Doppelgangers, Mind Flayers, and Umber Hulks.
Initiative: not included anywhere in the rules. It can be argued the initiative from Chainmail was a part of the rules but since that booklet was not in the box I'll still count it as an omission.
Missile Fire Ranges: fortunately, missile fire ranges were rarely an issue at first because most of the adventures were underground. Later, I just looked up the range for a longbow in the Encyclopedia Britannica and applied it to everything. Not very scientific perhaps but it worked just fine for my campaign.
Combat Example: this omission was remedied quickly with an example of combat in the official FAQ. Though combat was rather simple to run, writing an example for the rules might have highlighted to the co-authors the lack of certain information (such as initiative or missile ranges) in the printed rule books.
Psionics: added in a later supplement, the lack of psionics wasn't a stand-out at the time. It's probably more notable to a person familiar with later versions of the game.
Guidelines for Awarding Experience Points: they are actually present, but one must read carefully to spot them. The rules are very clear that 1 experience point (XP) is awarded per gold piece of treasure recovered. This is how players gain the most XP. The secondary method is defeating monsters in combat, here the rules are not quite as specific. Still a careful reading of the text yields the formula 100 XP per Hit Dice of opponent defeated. This was heavily revised by Gygax in Supplement I: Greyhawk and one is left wondering if the 100 XP per Hit Dice ruling is from an earlier draft of the rules and never meant for inclusion.