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.
The reaction of baking soda and citric acid (both are easy to come by and safe) in water does cool the water noticeably. I have tried it multiple times, and while it does not reach freezing, it will reliably reach $6\ ^\circ \mathrm{C}\ \left(43\ ^\circ \mathrm{F}\right)$, which is cold to the touch. 


  Add 4 teaspoons each of sodium bicaronate (baking soda) and citric acid to a cup. Then add the smallest amount of water you can and start stirring!


You can tell a chemical reaction is occurring because a gas is produced:

$$\ce{3NaHCO3 + H3C6H5O7 -&gt; Na3C6H5O7 + 3CO2(g) + 3H2O}$$

But, wait! We want a temperature below freezing! It might seem a little like cheating, but the reaction still works. Carbon dioxide bubbles are still produced, and the temprature gets down to around $-6\ ^\circ \mathrm{C}\ \left(21\ ^\circ \mathrm{F}\right)$.

If you do not have a thermometer, you can prove the second version is colder than the freezing point of water by doing the following:


Get a small, flat piece of wood and dampen the top surface of it.
Do the reaction in a glass, using 4 teaspoons each baking soda and citric acid and replacing the water with crushed ice.
As the temperature drops, the water between the wood and the glass will freeze, freezing the glass to the wood. If you lift the glass, the wood will stick to it.