Old English streaw "stems or stalks of certain cereals," literally "that which is scattered or strewn," related to streowian (see strew), from Proto-Germanic *strawam "that which is scattered" (cf. Old Norse stra, Danish straa, Swedish strå, Old Frisian stre, Old Dutch, Old High German stro, German Stroh "straw"), from PIE *stere- "to spread" (see structure (n.)). The notion is of dried grain stalks strewn on a floor as carpeting or bedding. As a type of what is trifling or unimportant, attested from late 13c. Meaning "hollow tube through which a drink is sucked" is recorded from 1851.
To draw straws as a means of deciding something is recorded from 1832. The last straw is from the proverb of the camel. Straw poll is from 1932; earlier straw vote (1866). Straw hat first attested mid-15c. To clutch (or grasp or catch) at straws (1748) is what a drowning man proverbially would do.