Banana peels contain potassium - which helps tomatoes resist disease and pests, help fruit to develop, and just generally strengthen your tomato plants. The phosphorus in the peels promotes more blossoms and hence - more tomatoes! The calcium helps roots to develop.
Eggshells keep the soil a bit acidic and help prevent blossom-end rot.
To make the fertilizer -
Collect eggshells and banana peels for several days. They get a bit smelly, so keep them in a zip-lock bag or a plastic closed container.
I pre-crunch the egg shells in the zip-lock bag and cut the banana peels into small pieces. Remove the tough stems.
Throw the shells and peels into a blender with about a cup of water. You can add more, if needed.
Blend until fairly fine.
Sprinkle around your tomato plants and gently work into the soil a bit.