In TES IV: Oblivion, you don’t have to buy a house nor join a guild/organization to have access to containers where you can safely store items, without them being reset every few in-game days.
Aside from containers in bought houses and guild/organization-provided containers, are there also similar ‘safe’ containers in Skyrim? Where are they located?
For example: The container, Jauffre’s chest in Weynon Priory in TES IV: Oblivion (other examples here), can be used without joining a guild or buying a house.
When you join a “college” or a “group” like Winterhold Academy or company in Windhelm, they give you a “dorm” room.
When you notice that some room might be yours open the console (tilde key) click on wardrobe to select it and type
IsOwner and you should see who it belongs to exactly. If it is you, then it is a safe place to store your items.
Also to make sure you can put item in container and go away for 48h that is the time items know to disappear.
Note:aiming at bed and seeing if it is red or not is easy and quick way,but it is not the most accurate since you can sleep in some beds even if you don’t own the cabinets…