If you are using a firepit or grilling somewhere and you're allowed to leave behind charcoal behind (on the beach/etc.) and you're trying to find find whatever possible to fill with water and dump over the charcoal/wood and have to make several trips, lining the INSIDE of the charcoal bag with a thin enough plastic lining so that if there is a nearby water spigot or lake or ocean you can dip the bag in the ocean (or fill it up with water from the spigot), good enough for two or three uses.
We've had this problem before; we're at the beach grilling out, using the firepit and we never remember to bring a bucket to get ocean water to put out the fire quickly without having to make quite a lot of trips.
I understand this also changes the price point of the already low-cost so that would be one problem.
1. Coat the inside of the bag with a thin plastic lining (little enough to break down in the trash, but "thick" enough to hold water, but "biodegradable" enough to recycle/burn through normal.
2. Another problem is people usually burn the bag in the fire when they're done using it. And if you put the hot coals in the bag it would melt through the bag/burn through the bag.
3. I don't know if someone would wash out the coals, then bag the coals in the same bag, but if they sogged down the coals that plastic film would keep the ash from sogging through the bag.