Essentially, whatever takes your fancy, I would say, but you will need a firm surface below the gravel, or material of your choice, to stop the table and more particularly the chairs sinking into. I would suggest a layer of hardcore, compacted and levelled, topped with weed control fabric. This can then be covered in your chosen 'topping'. The weed control fabric will serve 2 purposes - weed supressant and keeping your topping from mixing in with the underlying hardcore. When choosing the topping, bear in mind what it will feel like to walk on, particularly if you go barefoot - small pieces of gravel can be painful and large pebbles will not give you a smooth surface for anything to stand on. I like the idea of slate chips - it comes in various colours and lays flat.
Other GoYers may of course have other/better ideas.

Personally, if its for a table and chairs, I'd go for paving - whether that's paviours, granite setts, or slabs of some kind is up to you. You will need an area 8 feet square as a minimum to accommodate a small table and chairs, larger if you have a large table with more than 4 chairs.