What not to plant together in a container raised garden???

Answer 1

Unfortunately, companion planting has not withstood the test of scientific studies. That said, giving a plant adequate spacing for root growth and to prevent shading of adjacent plants is important.
Some recommend planting top-growth plants like tomatoes next to tuberous veggies like potatoes, carrots and beets. If you are hoping to plant your veggies close together, look up Square Foot Gardening. I found a webpage that has good info on this approach. https://www.ag.ndsu.edu/publications/lawns-gardens-trees/the-facts-of-square-foot-gardening

Answer 2

These articles will help you.

https://www.gardeningknowhow.com/edible/vegetables/tomato/tomato-plant-companions.htm
https://www.gardeningknowhow.com/edible/vegetables/pepper/pepper-plant-companions.htm
https://www.gardeningknowhow.com/edible/vegetables/potato/potato-plant-companions.htm