To start seedlings I save toilet paper tubes. I never put these in the recycling bin as I can use them to start my seedlings in and then plant directly into the ground where the cardboard will decompose without any harmful contaminants added to your soil. It's so much easier to plant the entire container than to gently transplant the seedlings and easier on the plant as well.
You could also use newsprint to make your own planters, just remember not to use any paper with colored print on it as those contain toxic dyes.
Another cheap and easy is to use egg shells. When composting, animal products are not supposed to be composted. Egg shells are an exception but I still don't add them to the compost. Here is a complete list of what you can compost and what nutrients they will add to your gardens.
Last night I crushed egg shells, I have friends and family save their eggshells which I crush into a fine powder with a mortar and pestle. I store these in clean empty containers from mason jars to oatmeal containers until spring. Once I have planted my seeds and seedlings I sprinkle the crushed egg shells over the top of the soil As they decompose they add calcium to the soil for your plants but they also have another purpose I learned accidentally.
Many of my neighbors were complaining about the slugs in their gardens. The slugs are every where here except my garden beds. I had no idea why until one neighbor was looking at my beds and asked me what the white powder was around the plants. When I told her it was crushed egg shells she laughed and said that was the reason I didn't have slugs. They find the shells, even finely ground, to be sharp and avoid those areas.
If you don't have a mortar and pestle, don't worry you can grind up your shells in a blender or food processor.
So start saving items now to have a healthy and productive garden.
Do you do anything special to have a productive garden?