Short lengths of dried grass can also be used, though I have not tried this myself. Rolling paper masts around a length of wire will provide stiffness and the ability to straighten the mast if needed. Ships boats The appearance of ships boats can be greatly improved by forming the hulls into the correct rounded shape. Try this out on some scrap card first. Chemical blackeners are available from hardware shops and are more appropriate than paints.
Railings See above under railings.
Other parts Generic parts are also available, eg ladders, hand-wheels, etc. Replace any printed handrails with wire or plastic shaped to fit. A lot of ship models have printed railings lining the decks - these are acceptable and can be fitted if desired. However, proper scale railings can dramatically improve the appearance of a ship model and are not difficult to make and fit. Cut the railings to length, bend to shape, paint an appropriate colour and glue into place.