Folding Chairs and Stools
Chairs that hang on a hook, stools that nest, and counter and bar stools that fold flat when nobody's sitting on them.
The useful rule: allow 600mm of table edge per person, and 900mm behind a chair to push it back and stand up — 1,100mm if someone has to walk past. A small room usually only has 600mm behind, which works, but everyone has to stand up at the same time.
Folding chairs live in the gap beside a wardrobe or on the back of a door. Two out for every day, four more in a cupboard, is how most small flats handle having people round.