I am currently in the middle of The Lost City of Z by David Grann (
Goodreads link), a nonfiction story about early 20th century exploration and it got me thinking about the pretty wide gulf between what a real world adventurer is, and what most RPG adventurers are.
I'm glad you made this thread, because I've been working on a OSR system that is exactly this. It's been on my mind for a while. I don't have anything final to share but I can share some general thoughts.
I think the idea, first of all, is just killer. The literary history of adventure gaming and expedition stories or historical expeditions are intimately linked. Going back to
The Odyssey, or Jason and the Argonauts, and the Polynesians or the Vikings or the search for the Source of the Nile, or Lawrence's march across the desert.
The main shift to make Expedition D&D (my term) work, imo, is to change the party size. If you have 4-6 heroes then dying of disease or starvation is not fun. It is too brittle: if it happens you lose based on something that is essentially tangential to the main game (dungeon crawling etc.) That means tracking supplies is not fun, nor gameable, because there are no real stakes.
I think you need to embrace having a larger party--say 10-50 people. A few of these are hero characters, some are retainers, some are porters. Overland you have big combats including the retainers. When you get to the dungeon you switch to playing just the heroes. If the heroes die you have retainers you can promote so players get to keep playing.
Obviously managing bands of this size is challenging, so you need much simplified combat. The way I run it, basically everyone gets a d20 + X to hit and rolls d6s for damage. I mean every weapon does a d6. The game is about expeditions, not weapon choices...so we simplify there.
If it gets too large then mass combat rules may be in play. I haven't needed them yet with sizes of 15-20 retainers.
Another change is too sharply limit the advancement of the heroes. The system I run caps out at 4th. There needs to be enough variance so lv 1 heroes are worth multiple retainers, but you can keep 4th level characters and retainers on the same battlefield. That means limiting complicated spells and abilities.