You can select an entire bin's contents then deselect just the bin itself. The only bin/barrels I ever sell are the (inferior) ones that aren't made in my fort, just to get rid of them.
The issue however is that by laws of priority, when shift-clicked to move all your accessible goods for trade in the menu, it clicks the umbrella bin first, additionally by mis-click the bin can be selected and your previously selected arrangement of goods lost
And when i have 100+ exceptional mussel shell bracelets to sell to some gullible poor mug via my seafood production lines (I'm quite fond of bone-crafters really), it's a real workout to click all the contents. Selling the bin also can be a clincher for additional profit in the traders aid (in addition to metals like zinc and aluminum being light enough to not eat valuable time hauling) to make them like you more even if you have diddly squat to offer them (say if a unfortunate accident occurred and a FB battered your food/trade good industry workers into dust)
Elves barely comprehend what charcoal is (obviously not enough to get disgusted and pretty much become a sulking civ in terms of behavior), let alone the methods to make metal. And im not really sure what you're doing or how you're doing metal wise if you can't make enough to import meltables and a reasonable amount of ores to run workshops to replace what you lose (buying up entire caravan food supplies in bulk to fuel more lavish and exotic kitchen meals for instance as a example)