ditty bag n.

"small bag used by sailors for needles, thread, scissors, thimble, etc.," 1828, nautical slang, of uncertain origin, perhaps from the alleged British naval phrase commodity bag. Hence also ditty-box (1841).

Every true man-of-war's man knows how to cut out clothing with as much ease, and producing as correct a fit, as the best tailor. This is a necessity on board ship, for the ready-made clothing procured of the purser is never known to fit, being generally manufactured several sizes larger than necessary, in order that it may be re-cut and made in good style. [Charles Nordhoff, "The Young Man-of-War's Man," 1866]