There are a countless number of free science experiments out there. Just think about the stuff you have around your house. There is no need to go out and buy lots of expensive items to create a great science experiment. You can do many experiments with water or food with items you already have in your home, such as to find out what effect salt is the boiling point of water. For this experiment, all you need is a pot, water, salt, measuring spoon and thermometer. Boil some water, test temperature, and then add one tablespoon of salt in boiling water, stir, and test the temperature again. You can add a few tablespoons (one by one) and test the temperature of boiling water for each scoop of salt. Be sure to take your results so you can compare afterwards.
Or, if you want to free science projects with food that you can try and see which place is best to store the fruit to keep it freshest longest. For this, all you have to do is get a few pieces of fruit and put them in various places around the room, perhaps one in the fridge, one of the dining table and one in the cage. Then wait and see what piece of fruit goes bad first and take the results. It does not take much thinking to free science experiment that you can pursue in your own home, or outdoors where you can experiment with bugs and plants.