A wagon is my favorite gardening tool. I had a little red wagon for years and a few years ago, got a flat bed garden center type wagon.
I use it to move large bags of soil, bird seed, dog food. We've hauled heavy concrete bird baths.
I set 5 gallon buckets filled with water and doodle them around the yard to water my plants.
I carry my tools, gloves, water bottle in the wagon and while working in the garden if I need a break I can use the wagon to sit on.
When kiddos come to visit, they can play with it or ride in it too.
If a gardener doesn't have one, I will recommend they add it to their most valuable tool list.