Well, it doesn't have to be a five gallon bucket. Some are smaller. All come with lids, and something inside them, which one is purchasing. The bucket is just the packaging.
But a five gallon bucket can be so much more than that. I have long wondered at how casually people dispose of these. They are tools, to me.
I first got seriously involved with five gallon buckets when I was spending a lot of time at a house that had a back yard across the alley from a grocery store, with all of its attendant trash bins. They threw out their bucket packaging on a regular basis.
Most of it was from the bakery. Lots of icing buckets. Occasionally garlic butter.
I learned pretty early on not to try to clean all of this residue out with soap. You scrape first. This stuff is greasy. Uses up a lot of soap.
Most people are more familiar with these buckets as containers for paint & other home improvement substances though, I would guess. But what I had was a grocery store's trash bins, a garden and a compost heap.
Just about anything you need to collect and work into your garden or compost heap can be easily managed with a five gallon bucket, including water, if you're short on hoses, and a wheelbarrow seems like overkill for the task. In fact, you can perforate them and use them as slow watering devices. You can set them by your roof (or elsewhere) to catch and store rainwater, too. And if you get a late frost, you can put them over your tomatoes to protect them from up to several degrees of it (put a rock on the bottom if it's windy). And I bet you could make a perfectly reasonable worm bin out of one, with enough holes drilled, kept in the shade and appropriately filled with worm substrate and fodder.
Also, you can make planters out of them! But in this case, you want to make your holes in the bottom a bit larger, and maybe offset around the edge of the bottom too, like commercial pots have their drainage holes.
Since these buckets are white, that especially lends them to use as planters in hot climates, as the white coloration will reflect heat, while black plastic pots will absorb it and often dry out much more quickly in consequence.
To make the holes, you can use a soldering iron and just melt 'em out, but if you do, do it outside with some breeze, as these are toxic fumes you really don't want to breathe.
Where I live, we have a lot of pecan trees. More ways to use up all of your buckets.
But wait. I lie. My first experiences with the myriad uses of the five gallon bucket was when I worked with the American Tarantula Society, and we made pitfall traps with them. Again, you perforate the bottom, so rainfall won't drown your catch before you collect it. (Edit: also it's good to put a rock in there, in case it rains a lot fast).
After burying the bucket with the top at ground level, you make a little top out of a square of plywood with shims. The critters you're looking for walk under the plywood and fall into the bucket.
We were looking for vinegaroons at the time, but did occasionally catch an interesting snake. It's important for people who want to do this, to check your traplines frequently, so you are not inadvertently killing off the wildlife, and also of course make sure you release anybody who falls in there who is illegal to collect.
Let's see; what else? Well, they make good trash cans, or kitchen compost collectors, or general water storage devices in case your local water system collapses. You can even turn them over and sit on them if you don't weigh too much.
What a funny country we are, that we treat such useful objects simply as packaging.
(posted from an original draft at Right of Assembly)