So I'm a little confused now. On page 307 it says the interact action is used to grab a stored object. But on page 175 it says 2 actions to retrieve an item from backpack and if your backpack you need another action to take off your backpack first.
What is the difference here? When do you use 1 action to get stuff vs 2 actions?
So if I'm wanting a wand or a potion or a backup weapon what actions does it take to get these?
Many items can be "stored" where they are easy to get. A dagger in a sheath. A potion in your belt pouch. Wands in a quiver. The generic action to retrieve such an item is just a single action.
Some containers like backpacks and satchels (and I would would assume sacks should be included here too) are much larger and have lots of junk cluttered in there. If you've ever seen my wife look for her keys in her giant jumbo purse - basically a satchel - you'd know what I mean. I think sometimes it takes her 8 or 9 actions to find anything in there but Paizo is being generous in limiting it to just 2 actions.
So, getting a conveniently stored item is always 1 action unless that item is tossed into a larger container like a backpack or satchel in which case it takes 2 actions.
So it is to your advantage to "store" stuff you need in a hurry in locations that are easy to reach and access so that you can get them in just 1 action. Keep your wands in a simple quiver, your potions in belt pouches (or a potion bandoleer), and your backup weapons in belt sheaths or back scabbards or hanging from your belt on a thong or whatever fits the type of weapon.
Keep the junk you use in camps, or in special downtime activities, in your backpack or other containers where quick access is not a concern.
So how many items can I have stored? Can I have 3 potions? 4? Like for an alchemist this limit I imagine would be important and probably reached for how much stuff they want in easy access. Is there something in the rules about how to decide if something can/is stored or in backpack?
For the upcoming playtest module one of my players is asking about this because he wanted to test a high level alchemist and how their combat economy is, but now we're stuck on if it'll be 2-3 or 1 action to draw his premade bombs
I don't know of specific rules regarding how many.
I keep it simple. If it fits in a pouch, and the PC might want it instantly available, then it's in a pouch. Too many for one pouch? Then he has more pouches. If it's too big for a pouch (like, say, a tent) then it's in a backback. If it's not needed instantly in the heat of combat (like, say, flint and steel) then it's in a backpack.
If some player is abusing this rule with scores of instant-access items then maybe I'll have a chat with this guy about trimming his list down to a dozen or so and putting the rest in a backpack. Hey, wizards might know every spell but they can't prepare all of them each morning, so why should they have every possible potion at their fingertips?
Regarding alchemists and "storing" their items that they create with their core class feature, I use this rule, which starts with a question: How many "class feature" spells can a wizard/sorcerer/cleric have in his head, and how many are in his backpack?
The answer of course is all of them are in his head. Every spell class feature a wizard/sorcerer/cleric can prepare and/or cast today is in his head, immediately accessible without any extra actions (just the requisite actions to cast the spells). Maximum availability of class features.
So, for alchemists, I rule that their class feature items work the same way. They're all at the most accessible they can be. Maximum availability of class features.
Is it weird to envision an alchemist walking around with 30 vials hanging from their belt by short loops of twine, at least a couple dozen pouches containing any number of readily available alchemical stuff, bandoleers layered over other bandoleers, all containing even more alchemical stuff?
Yep.
But I'm not going to bury the alchemist's core class feature behind arbitrary "storing" or "bulk" rules when no other class has that problem (except rangers who want to use snares or bards who want to play tubas).