Inanimate life companion
The best fit I can think of is 'trusty'.
"Joe picked up his trusty knife, his daily companion for many years."
While it is not an exact description, the examples you give might be considered to have totemic significance to the owner
- (anthropology) of or relating to an object, species of animal or plant, or natural phenomenon symbolizing a clan, family, etc, often having ritual associations (in some societies, esp among North American Indians)
- of symbolic importance
This would be especially true if there were some tradition associated with the crafting or adoption of the object.
Another term that approaches the concept is iconic, associated with this definition of icon
someone or something regarded as embodying the essential characteristics of an era, group, etc