it was her habit to build up laughter out of inadequate materials.

Steinbeck’s line sketches a character trait: the ability to manufacture joy when circumstances offer little to laugh about. “Inadequate materials” suggests scarcity—thin reasons, meager comforts, or even hardship—yet the person described can still “build up” laughter, as if it were a craft or shelter constructed from scraps. The phrasing implies resilience and a kind of imaginative generosity: humor becomes a deliberate act of survival and social care, not merely a spontaneous reaction to something funny. It also carries a faint irony, acknowledging that the raw ingredients for happiness may be objectively insufficient, while admiring the will and artistry required to transform them into communal relief.