For example, let's say I go into some house and find a pack of cigarettes inside a file cabinet

Will that same pack of cigarettes be in the same place every playthrough or would I find something else there every time?

As I understand it, and it was this way in previous games for the most part, items in containers are "spawned" from a random list. Items that persist in the world proper will likely always be the same. Playing through the tutorial a couple of times seems to confirm this.

Generally junk items in containers or a creature's inventory are spawned from a list. There are exceptions such as things that have a 100% chance to appear and specific quest items. Anything hand-placed on a shelf or similar is persistent between games.

Objects in the world are hand placed by the devs but objects in containers are random yes.

Actually Skyrim introduced a new feature called "Dummy objects". Wherein a dev placed a temp object, then assigned it a leveled list, and the game picked from that list when it spawned objects, just like a container. They used this sometimes for potions, weapons, armors, etc.

I'd assume Fallout uses this as well in many places. Some loose items are hand picked, but others are leveled, as are most containers.

I suspect that something simular to the Skyrim system here

http://www.uesp.net/wiki/Skyrim:Respawning

is how it works

what do you mean by "leveled"?

That's what they're called in the engine. A "Leveled list". It means item within can be sorted and chosen based on player level, though they don't have to be. Most items in the game (like junk) is generally set up without taking player level into account, while some choice items (like armor and weapons, usually) are.

yes its random

i played 3 or 4 hours on both ps4 and xbox one, and i found more bobby pins etc on my xbox on game, whlst looting all the same stuff along the same route.

Probably, and the Skyrim system was nice, in Oblivion it was just junk in the open.

One Suitcase has spawned the Red Dress, Combat Fatigues, and a third piece of "pre war" Clothing when I was playing with Character Creation when exiting the Vault. Each character has gotten a different Clothing item.

Cool, I didn't know that, I haven't messed around in the creation kit since the Fallout ones and not done any modding myself since Morrowind