When doing a cheap garden- Don't buy plants unless they are dwarf trees. $3 for 50-300 seeds or $3 for 1-4plants. Seeds are way cheaper and very easy to start. Only get organic non gmo seeds.
Make sure food trees/bushes you get are self fertile/self fruiting meaning you only need 1 and not 2 to have fruit.
Basic tools you need might be a large digging shovel, besides that you don't really need others. A hand digging shovel and good quality garden gloves are nice except a large shovel or maybe some kitchen tool could work also, and any sturdy gloves can be used.
Take back items you got that you don't need.
Compost. It's free and simple, just put decomposables, food scraps, plant materials in a pile outside.
You could buy some red wiggler worms and add them to the compost, as long as well cared for, they should increase in numbers, they help break down compost faster and their poop adds nutrients.
Coffee grounds and banana peels should be composted first. Composted banana peels and composted coffee grounds help. Banana peels and compost in general can be covered with some dirt to help keep flys/bees/bugs from being attracted to it.
Finished composted looks like soil and doesn't smell bad. Composted coffee grounds and composted banana peels alone are probably not enough nutrients, you should have a wide variety of nutrients for the soil. You should have a variety of composted: food scraps, plant materials, and worm castings or composted manure.
Collect as much rain water as you can and use that for watering the plants.
If your soil is hard and clayey, a good quality potting mix can be added to loosen it- get high quality stuff to help loosen the soil, it's basically a 1 time application, at least get some to test out a small area to learn the difference how much it helps the plants do better. If the soil is hard and clayey it's hard for the roots to grow.