Indeed; in the old days they had no plastic, so the bowl was the only dry space they had. Sometimes the monks would end up spending a rainy night without any cover. Extra robes, books, papers and the like would be packed in the bowl. Ajahn Mun, according to legend, used to carry a copy of the Abhidhammatthasangha with him on tudong (don’t ask me where I got that from!).
It might be possible to learn something about bowl sizes from the remnants of Northern Black Polished Ware:
