My own OD&D campaign is based on just the 3LBBs, plus some house rules. These were informed by lots of different sources, including Holmes Basic, BLUEHOLME, Philotomy’s Musings, the Delving Deeper rules, the OD&D FAQ from Strategic Review magazine, and various bits and pieces mentioned in games, forums or blogs that stuck in my memory. Most recently, I’ve read through the Seven Voyages of Zylarthen (SVoZ) and pulled in spending gold for experience from that. Here are some highlights (last updated 2015-06-02):

• I don’t like the stat/hit dice/bonus inflation that was ushered in with the Greyhawk supplement, so I keep d6 for all hit dice and d6 for all weapon/monster damage. I only add minimal bonuses/penalties for strength, and keep the other ability bonuses as-is.
• Magical healing is downplayed, with binding wounds available to all PCs along with the Warden class’ healing poultices. I prefer not to use Clerics, but I keep the option available as some players really like them, and at least this way the Cleric can be something other than ‘the party healer’.
• I really liked the idea of gold being used for experience, but only if it is spent (from SVoZ). This avoids the problem of “where do I keep my mountain of gold?” that is so often hand-waved away as PCs get to higher levels, and gives PCs a choice if they want to buy pricier items like scrolls or potions – gain experience, or spend it on cool stuff?
• I love the scroll/spellbook rules from Holmes and BLUEHOLME, so I incorporated those as-is.
• I don’t like race-as-class (as much as OD&D did not ostensibly have this, giving a Hobbit or Dwarf one ‘choice’  for a class, and the odd Elf multi-class are all pretty much the same thing). So I allow other class choices for non-humans, including Dwarven Clerics and my own Rogue and Warden (a Ranger minus the spells) classes for Hobbits and Elves, respectively. Elves can also choose to be just FM or M-Us if they wish.
• I like the encumbrance rules from Men & Magic, particularly that ‘Miscellaneous Equipment’  is a set weight. No need to count every torch and iron spike. I just don’t like that the max encumbrance is 300lbs worth of gold coins. So I just changed the weight of a coin from 10 coins per pound to 20. This effectively halves that weight allowance while still allowing lots of coins to be carried.
• I use the Delving Deeper interpretation of the FMs multiple attacks being based on normal-types of less than 3HD.

You can download the OD&D house rules document in PDF or Libre Office format.

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