What can I add to my buckets to help my tomatoes and cucumbers produce

I would probably look for a vegetable plant food that you give periodically throughout the plant's life.

I'm not sure what size buckets you have, but be sure you are using quality soil and you may want to use a fertilizer like Miracle Gro.

https://www.gardeningknowhow.com/special/containers/growing-vegetables-in-buckets.htm

If you used good potting soil, use a fertilizer for tomatoes and vegetables. If your buckets are large enough for good root growth, you should be ok. Since your tomatoes are in basically a pot, you will need to get a calcium supplement to prevent blossom end rot, it is very common due to lack of calcium in the soil. The easiest way is to find a foliar feed calcium supplement and spray the leaves as the tomatoes start to turn from green as they start to ripen. The spray provides much faster absorption of the calcium into the leaves, stems and then tomatoes. Make sure you support the tomatoes and cucumbers as they grow.

Epson salts in the watering can. Directions are on the package.

Hello. I love to mix in tomato tone. I mix a little in at the base of the plant about once a week. It works great and has a lot of calcium in it which helps prevent diseases, and tomatos love!

Miracle Grow for Vegetables, and a marigold in each tomato bucket to help repel bugs. And an odd eggshell or coffee grounds. ☺️

A few weeks after planting ours and herbs we made a 'tea' out of coffee grounds and cleaned, crushed eggshells; threw them in the blender and added water. Strain it all and add to a garden sprayer. (toss the grounds and eggshells strained out away asap as they're going to stink! ) Breaking down the eggshells lets the calcium release faster so the plant can use it. We spray the base of all our herbs and plants every 2-3 weeks. Works like crazy.