This is a simple suggestion for something that is a bit annoying when handling large amounts of certain containers (like wheelbarrows or barrels) inside vehicles like wagon, knarr or even the packrack on a bull.
Sometimes we take several wheelbarrows or barrels within those vehicles for major hauling operations or massive operations to collect a resource, and it is always annoying to pick up the barrel or wheelbarrow to check if it's filled already or empty. This can be slightly mitigated if you're alone (and organized) but it's always chaos when there are more people helping and any organization starts to get messy.
So the simple suggestion is: make the little "icon" of the item inside a vehicle (or whatever else like a shack) be different if empty. For example, the wheelbarrow icon appears as the loaded wheelbarrow - make it appear empty if it is empty. That way you can easily open a knarr with 50 barrels and tell which ones are filled with water already (for example), or when transporting stone or dirt with a wagon you can look at all the wheelbarrows and know which ones to fill, which ones are already filled, etc...
Not really a big deal, more like a Quality of Life improvement
