One player wants to pass a potion to another player in the middle of combat. What kind of actions are needed?
Free action for the giver, move action for the receiver
The closest I've seen the rules come to this is the general rule for manipulating items:
In most cases, moving or manipulating an item is a move action.
Examples of "moving or manipulating" that relate to this are:
- Draw a weapon
- Pick up an item
- Sheathe a weapon
- Retrieve a stored item
However, that's just one side of the equation. Two people are involved in passing along an item. And we have this rule:
Dropping an item in your space or into an adjacent square is a free action.
Since picking up an item off the ground is a move action, one character just needs to drop the item in question into an adjacent space, and the other character can move to that space and pick it up.
In light of this, it would be silly to require a move action to "manipulate" the item from yourself to your ally. I would rule that handing over an item is a move action for the receiver and a free action for the giver.
But only if it's already held
Don't forget that since it's a move action to draw an item out of a backpack, belt, etc, the giver may need additional actions in order to actually get the item into his hands.