In my campaign, I've been using Delta's stone-weight encumbrance system, and found it a lot friendlier than the traditional coin-weight system. However, in play we found that tracking items getting used or discarded was still troublesome. Particularly since under Delta's system, a number of items are rated as different fractions of a stone, and these on-the-fly calculations were not going smoothly.
So I offer this streamlined method for encumbrance. It is, obviously, based off of the most basic armor/movement system presented in B/X, with a small addition designed to make Strength matter and to promote a little more careful forethought and planning before each delve.
Base encumbrance is determined by armor:
None = Unencumbered (120'/turn).
Leather = Light load (90').
Mail = Medium load (60').
Plate & mail is Mail + 1 heavy item.
Each character will have a carrying capacity determined by Strength. Carrying the limit of this capacity will increase load by one level.
Heavy items count against this capacity. This includes shields, heavy weapons, batches of treasure equal to 500 coins, a loaded backpack, and miscellaneous objects that weigh 1 stone or so. Some items that are not heavy but awkwardly over-sized (such as a 10' pole) may also count against this limit.
Normal equipment doesn't count against carrying capacity. It is limited by available carrying space. Up to 15 small items can fit in a backpack or shoulderbag. (With 5 or more items, it counts as loaded; 100 coins of treasure count as a small item, too.) One waterskin can be safely strapped to the backpack; spares take up room inside.
Very small, light items (such as a mirror, tinderbox, or chalk) can be carried more readily in a belt-pouch, along with a single small item (or up to 100 coins). Items in a belt pouch can be pulled out with relative ease, compared to rummaging through a backpack.
Weapons are limited as follows: 2 spaces on the belt, one space on the back or shoulder. Daggers can be carried in additional spaces, such as boot-sheaths. A bow and quiver can fit in the same space. Heavy weapons (such as a battle-axe or morning star) will also count as against carrying capacity.
Treasure is rated at 500 coins per stone-weight, with 100 coins equal to a small item. A gem counts as 1 coin, while any item of jewelry (and most magical treasures) will count as 10 coins. Treasure will need to be carried. A small sack can carry 1,000 coins (or 2 stone), while a large sack can carry 2,500 coins (or 5 stone).
Effects on game-play:
1) Equipment must be planned carefully, as only a limited amount can be brought on any expedition. This might increase the value of hired bearers.
2) Using up or redistributing ordinary supplies will not usually affect one's encumbrance. (We often found that after the party had burned through several torches, their encumbrance could be recalculated to a faster movement, but nobody ever noticed.) This reduces the need to recount on the fly. I anticipate that the main point where encumbrance need be re-checked will be when a sizeable treasure has been recovered.
3) I haven't yet got a solution to the "carrying fallen comrades" dilemma. Under the coin-weight system, humans were defined as 1600 cn; under the stone-weight system, I had defined humans as 12 st; thus a character carrying a fallen ally would have to lug that ally's encumbrance+12st, which worked pretty well. I have no doubt there's a similarly elegant solution to this one, i just haven't found it yet.