Knick-knacks found in stores of thrift Souvenirs from time away Trinkets given as a gift Useless but to decorate

I’m small and dark, yet ground for bite, often beside my friend in white.

I hold secret words and valuable letters, but I am only secured by trust. I can also hold junk, but I'm not a trash bin. Sometimes large, sometimes small, sometimes flat, sometimes... less flat. Take away my last letter and you'll discover what I do to my contents.

I am a deep, man-made hole in the earth, created by tearing away rock, stone, or sand. I hold secrets of the ground below, yet when I am filled with water, I become a place for a swim. What am I?

When pyjamas rule and shoes retire, I help warm your feet beside the fire.