I have been travelling quite a lot recently and now go on the train everyday. One of the things I do not leave home without is my stainless steel water bottle filled from home. I have found that if I leave it in the fridge overnight before going out the following morning it stays cold all day.
This has saved me buying water when out and I have often found places where I can fill it up for free. Since it stays cold all day it also came in very handy for staying cool on the Tube, which over the past few weeks has been at a temperature of over 100F on some routes !
Saving my pennies and my cool, so it's a great addition to my kitchen !