depends if you mean in your inventory or in your storage, I have gotten alot of wood, iron and twigs to last but in my inventory usally the matrials for tools can run out
Normal wood or hardwoord. I have stacks of softwood in my storage but I don't seem to go through it quickly so I have a bunch saved. I don't like chopping trees so woods are the main resources I run out of and just chop as needed then stop.
I keep running out of hardwood because I keep crafting the log furniture and country fences I wish we could trade one type of material for another, like an NPC were we could exchange softwood for hardwood or something