One of those things which she has for sale by the sea shore

Tall and thin, jutting high into the sky, you can find these on castles, in no short supply.

I fill with people every morning, then slowly empty out. Screens glow beneath fluorescent lights, while printers hum about.

Sweet delight from the cane or the beet, A kitchen staple that makes life taste neat. In pies and cakes, you’ll often be found, A sprinkle of you makes the world go 'round.

I once stood tall among the trees, Now waves carry me with ease. Weathered, worn, and bleached by sun, I travel wherever the tides run. What am I?