Material Pools (3.5e Variant Rule)
From D&D Wiki
Material pools are a simplified way of keeping track of materials used by certain abilities and skills. Instead of buying and keeping track of base components, gold is instead spent to acquire an amount of stock in a relevant material pool. When a character needs a component or base materials, instead of keeping track of lots of different items he instead deducts the cost from the appropriate pool.
Replenishing a pool is just as simple. Any time the characters are in a town or city, or any other place they'd get the relevant base materials, they can spend gold to add value to one of their pools. Certain treasure hoards might also contain unspecified items that can be added to a certain pool that a character posses. For example looting the evil wizards alchemy lab might provide 10gp of Alchemy pool.
A character may have a pool for each craft skill or item creation feat that they possess. In addition spellcasters may also have a spell component pool to simplify the magic system. This last pool might require a PC to justify certain items being in the spell component pool. For instance, a PC might not have any particular reason to have bought a component to a spell that they do not know of or have an unusual or rare component.
Different pools represent different things so each pool has a certain amount of value that weighs one pound of weight. To calculate the total weight of the items a characters pool represents, simply divide its total worth by this figure.