A set of three or four steel bowls that nest into the space of one. They do more jobs per gram than anything else in the box.
Mixing flatbread dough is the obvious one, and flatbread is what makes a cupboard of tins into meals. But the same bowls soak dried pulses overnight, hold the rehydrating mushrooms, serve as a washing-up basin for a small pitch, and act as plates.
Steel rather than plastic because it takes boiling water without softening, does not hold smells, and nests without sticking together in the heat. Buy them with silicone or rubber bases if the choice exists: a steel bowl on a steel table slides while you are working a dough.
One of them should be big enough to soak a full bag of pulses in twice their volume of water, which is more capacity than people estimate. See pulse rehydration for how much water that actually is.