This is a subject that's near and dear. Charcoal is wonderful stuff and I'm tooling up to make it.
My wife is a potter and I want to make her a catenary arch kiln (and a wood fired pizza oven). It's going to take a lot of fire brick and the only way I can afford them is to make them. One way to make them is to mix sawdust with clay, form bricks, and fire it. When it burns out it leaves a porous brick that's made insulative by the holes formed where the sawdust was. Only, sawdust has a lot of moisture and organic compounds that make it hard and messy to fire out. Charcoal, however, is pure carbon and burns out quick and clean so it's a lot better than the sawdust that all the books tell you to use. You just need it in sawdust sized particles. For a more heat resistant brick there are other materials you can mix in along with the charcoal. One is called grog. It's a pre-fired clay that's expensive to buy but you can make it by crumbling up the bricks that you made with just clay and charcoal mix. You just need to mix in more charcoal so it's a weaker and more crumbly brick than you'd want to use structurally in the kiln. . . So, that's one use for charcoal.
There are health benefits to eating it. . . that medical grade that you have. That's another whole subject that I haven't gone into deep enough, yet, to separate out the wild claims from the real science.
And, of course, you can use it in a filter. Do you live in Flint? The bad news is that Flint is just the tip of the iceberg. Chlorine and fluorine are both toxic, and you know that they get added to city water supplies. If you don't do your own treatment you don't know what's in your water. Buy bottled water and chances are it was just taken from a city system. do the research and it will scare you. I take my water off the roof then filter it. You can't get completely away from city water without becoming a hermit. But, you don't have to drink only city water.
For the garden the term you want to search is terra preta. Here is a place to start. My wife is convinced that the pottery shards in terra preta is because the natives were ground firing pottery and discovered the agricultural use of the charcoal made during that process as a side effect. There is some controversy as to whether it's terra preta if it isn't made with a charcoal that's made at a low temperature. Biochar is the term for any old charcoal that you add to your soil. But, like so many have pointed out here, it does need to be activated with microbes and nutrients to get the full benefit. Run it through your compost pile before you put it on the garden. And, BTW, adding leaf litter from a local wooded area is a good way to inoculate your compost with the good soil microorganisms that thrive where you live.
The sawmill where I've been getting slabs for firewood has installed a chipper and they chip all their waste now, so I can't get slabs. . . but I can get the chip/sawdust mix that comes out of the chipper. Here is an easy to make stove that burns sawdust. You can find several versions on YouTube. I'm in the process of building one that combines the best features. One feature is that you can very easily modify it to make charcoal, like this.
If you want a larger setup, just for making biochar, check this out. And, again, you can see several versions on YouTube.
So, anyway, charcoal is great stuff. If you can get it for free I'd sure grab it. With a little research you can find good uses for it.