Any raw food from your meals can be included in what you add to your soil. Leftover salads, apple cores, banana peels or whatever you have will make a rich addition to growing the amount of soil you have.
All houseplants drop leaves or need pruning from time to time. Anything that comes off of a plant in your home can be added to the soil to increase its growth. Large dead leaves are particularly good for increasing the amount of organic matter in your soil, as they break down into small particles rich in nitrogen and other vital nutrients.
If you have a fire place you can add ashes to your soil as a great source of nutrients. Adding ashes will grow your soil fast, as it adds rich materials from burned wood. Make sure the ashes have cooled before you add them to the soil so that they do not harm any beneficial organisms.
Do not add any meat or bones to your soil. Not only will it smell bad, it will create an environment in the soil that is not conducive to good soil growth. Also avoid adding any cooked food since the natural enzymes that help to break down the material are lost during cooking.