Wanting to keep as much as possible out of the landfill we found a use for everything but the plastic support columns. The liner we cut up and stored to use later for something, perhaps as walkways in the garden. The plastic rim that went around the top we used to line around my herb garden which was planted using an old winter pool cover to initially cover the ground and kill the grass so the size was the same. The tin sides were cut up and picked up by a local scrap dealer. What a job all that was!
The remaining sand pit remained and we decided to turn the area into a great spot for garden bedding boxes. Already leveled flat and with great southern sun exposure it was the perfect spot for plants needing at least eight hours of direct sun a day. Being the boxes were on sand we wanted a deeper depth so used 12" wide lumber. These boxes are 8' long by 4' wide which is perfect for my needs. You don't want your boxes too wide or it becomes difficult to reach towards the center. We needed almost four yards of garden soil to fill them so to save money we ordered it to be delivered as a truck load rather than individual bags. It was a mixture of top soil and mushroom soil. What a delight to work with great quality soil right from the start!
With limited space, try to make the most of going up. Pole beans rather than bush beans, cucumbers and my birdhouse gourds all climb so the use of vertical supports really increases your possibilities. I even made use of an old wooden ladder for the gourds.
Think succession planting. If you plant onions in the early spring and pull them as scallions, that area can be later used for something else. By August when the summer squash and green beans may be dwindling you can plant turnips, spinach, lettuce, beets, kale, radishes, chard and winter onions. By October you will have room for planting some garlic bulbs and enjoy fresh garlic next July. When the garlic gets dug up there will be space for something else, perhaps a second planting of green beans.
Bedding boxes don't have to be used for vegetable gardens. You can have a beautiful herb garden. Get creative and have a themed garden. Perhaps one box can be for your cooking herbs, another box can be used for medicinal herbs, another can be for herbs used in crafts such as the Artemisias which are great for making wreaths. You can create a garden aimed to attract beneficial pollinators or for butterflies and hummingbirds. One box can be your night bloomers to attract moths. So even with limited space you can create your own, unique, individualized spot to call your own.