A nice question. First, I’ll assume that your thinking about living things.
The answer: no!
Our bodies are mostly made up of cells, but the gaps in between are filled by network of fibres, such as collagen, that are not part of cells. Also, about 1/3 of the (salty) water in our bodies is outside cells, while the hard material that makes up bone is also not in cells. This is similar for other animals.
Viruses aren’t cells (and don’t contain cells) but they’re also not alive. So, having cells seems to be a characteristic feature of living things on this planet, but most living things also contain parts that are outside of cells.
The answer is no – not everything is made of cells. Even in living entities, cells only make up a part of our system. The cells themselves are even made up of a whole range of things, drilling right down to the fundamentals of physics itself – cells are actually quite big in comparison to something like tachyons.