As an expat in a town full of expats, I'm sometimes the recipient of stuff people have not used up by the time they are on their way out the door.
Once in awhile these leftovers are appliances such as lime-scale crusted irons and hand-mixers that may or may not work...and once a TV (yippee!)
More often they are baking soda and baking powder, yeast, flour, sugar and spices. With Depression habits in my genes (that's The Great Depresssion) and not one to look a gift horse in the mouth, I now have three nearly full tins of Calumet baking powder and lots of baking soda - and even some powdered gelatine too. I know spices lose their flavour and flour gets mites so those are usually the first to go. Ditto yeast which I never use and which I assume loses its powers.
But how about the baking soda/powder and gelatine?
Do they ever go bad or lose their 'oomph'? (whatever that oomph may be, as I still haven't really figured out a use for baking soda beyond its ability to soak up odors...or a use for baking powder in this age of self-raising flour - per the other thread!)