Ketchup
Due to the naturally acidic nature of ketchup, bacteria are unable to grow and cause your ketchup to get soured as a result. It serves no purpose to keep it in the refrigerator. For a vast majority of people, the flavour is best when served at room temperature, I mean obviously.
If you live in a hotter climate, you may want to keep your opened ketchup container in the refrigerator until the temperature drops. Alternatively, if you only use your refrigerator on a regular basis, its lifespan will be increased, but remember you’ll have to enjoy your french fries without a room temperature ketchup, so I guess, not a good choice.