thermodynamics - Safe endothermic reaction that gets below freezing?

I have a project/idea I am working on but I am only 14 years old and I need some help.

I'm looking for an endothermic reaction that gets below freezing, but the chemicals before the reaction and after the reaction is over are safe to touch and safe for the environment. The reaction can be harmful to plant life, but only for a short time before it decays or whatever needs to happen for it to be safe. I do not want it to have long term effects.

Additionally, two important parts are that these substances need to be easy to obtain and need to not to be a fertilizer.