In my group, there is some confusion about how and with which action you use certain things in spellcasting. I would appreciate if someone could clarify these to me and point me to where these things are explained in the rulebook.
1) Material components. On the one hand, it seems that you have to have those in a hand to use them, since you can't cast spells with material components when pinned, on the other hand you do not seem to need to draw them as an action. Is my understanding correct that you have to draw them with a free hand, but that that is part of the spellcasting action (even for a quickened spell) and uses the same hand used for somatic components? But you cannot cast a spell with material components if both hands are full, even if that has no somatic components (e.g. from the Still Spell feat).
2) Metamagic rods. Do you need to hold them in another hand than the one doing the somatic and/or material components, or do you wave the rod Harry-Potter-style for the somatic component? Asked differently, can you cast a somatic components spell using a metamagic rod when you only have one hand free? How about a material component spell?
3) Potions, Wands and other items that effectively cast spells. Is my understanding correct that you first need to draw these as a separate action before using them as standard actions? Wands are drawn like weapons, but how about potions? Are they drawn with the 'Retrieve an item' action, provoking AoOs, or is there a way to draw them safely like weapons? What is the effect of a bandolier, seeing that getting stuff out of a backpack is the same action?
4) Scrolls. Is drawing a scroll part of using it, or is that a separate action?
1. That's basically how everybody that I've heard of has played it, but there's a bit of ambiguity about whether "preparing" includes "retrieving" that would have rather harsh consequences on spellcasters if the status quo shifted.
2. Barring any special text, you'd need the other hand free. A small price to pay for something better than a feat-on-a-stick, but annoying to staff users.
3. You have to retrieve most objects before you can use them, including wands and the like. If you mean the adventurer's sash, the only mechanical benefit is giving your character an excuse to have lots of small and different items worn on their person without having a zillion pockets or mini-pouches. For many games, this amounts to no benefit at all; for mine, it it quite useful for, e.g., a gunslinger packing ten kinds of ammunition who doesn't want to grab the wrong kind during a fight. But that involves GM discretion, as there's no rule saying you can't just fill your backpack with a hundred almost-identical objects and retrieve the exact object you want as a move action.
4. Again, separate action.
1. If you have a spell component pouch, drawing and using a material component is part of the action of casting the spell and uses the same hand that you use to perform the somatic component. A spell with a material (or focus) component requires one hand to reach and use that item even if the spell has no somatic component.
2. The rod must be held in one hand when casting. You can't perform a somatic component with the hand that's holding the rod. By default, casting using a metamagic rod requires two hands.
3 and 4. It's a separate action to take the item from where it's stored.