Plain rice porridge: rice cooked soft in plenty of water, with no salt or other flavour. Eaten at breakfast or when unwell, with pickles, salted egg, a fried dough stick or other side dishes.
If your stomach is upset, just have some plain congee.
Tips
culture
Just rice and water - the default 'sick food' across Chinese culture, the way chicken soup functions in the West. The bland, easy-to-digest baseline that everything else (咸菜, 皮蛋, 肉松) gets paired with.