The rule of thumb: Treasure value per PC should equal 1/2 the Party Average Level in Gold Pieces.
This treasure level assumes the module has combat scenes and that the
PC's will be using some of their resources to combat the adversaries.
Modules designed without combat scenes(*not* a combat module where the
PC's avoid combat by being clever) should only be "kitted out" at 1/3
the party average level per PC.
Production point treasure should be counted as equal to 1/2 its Production point value, in silver pieces. In other words, a paralysis gas poison (40 production) will be counted as 20 silver (2 gold) toward the cap. They are reduced from actual game cost because such items usually are only "treasure" for characters with appropriate skills.
One-shot magical items should be counted as 5 times the spell level in silver. Thus an activate life item (9th level) counts as 45 silver. As one-shot items are not common treasure and most likely every PC will not receive one, the value is slightly reduced. Additionally, both production point items and one-shots have the potential to be used against the NPC.
Hidden treasure (that may or not be found on the module) should only comprise 1/3 of the total treasure on the module and is counted at half value. (Example: A 5th level party of 6 PC's will have 30 Gold total treasure on an "average" module. If the Module author wishes to have a hidden chest in one room, that the PC's may actually miss, he should not place more than 10 gold of the 30 in the chest. As the chest is hidden, and difficult to find, the chest value is doubled. Thus this module has 20 gold on the monsters or readily seen and a hidden chest with 20 gold in it, bringing the total value of the module to 40 gold, but with 20 gold harder to find.
Permanent magic items may only be placed with Plot approval and are singular and not accounted for in this treasure guideline.
Placement of treasure can vary, but should either be "open" or "hidden", as above. Open treasure may be on monster bodies, lightly concealed, or given as payment upon module completion. It is entirely possible that PC's may overlook "open" treasure - the module marshal does not compensate them additionally for their oversight - the PC's may just have to go on another module if they wish to cap.