Is it ok to leave items in the trunk of a car?

I drive a 1999 Honda Civic and i was wondering is it okay to leave items like washer fluid or a case of water or anyone items (other than food) in the trunk. I do not have windows where you can see the trunk but i leave it outside of my house since there is no room in the garage and usually the temperature is around 20 degrees Celsius during the summer. Will it go bad or i should be fine?

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