General:
* Items
* Objects
* Possessions
* Belongings
* Stuff
* Goods
* Materials
More specific:
* For tangible objects: Articles, equipment, tools, appliances, furniture
* For concepts or ideas: Matters, issues, topics, subjects, concepts
* For events or activities: Occurrences, happenings, events, activities
* For people: Individuals, persons, beings
Informal:
* Stuff: This is a very versatile word that can often be used instead of "things".
* Junk: This implies things of little value or usefulness.
Formal:
* Entities: This is a more abstract and formal word that refers to things that exist as separate units.
Ultimately, the best synonym will depend on the specific context and the desired level of formality.