Short version:
Have the manager automatically queue up jobs to fill certain stockpiles. If a rock block stockpile has room for 10 more, they'll makes 10 "make rock block" jobs. If its a food or booze stockpiles, they'll keep it full automatically.
Long, detailed, how it'll work version:
Eligibility
Only certain things would work with this. Things that need designations, like stone, logs, plants from gathering/farming, meat from butchering, as well as other various things wouldn't work. I'll put up a list later.
Setup:
Two ways I can think of. First is to make a third option for existing stockpiles. In addition to the Allow and Don't Allow we have now, a particular item can be set to auto fill, and have a different color (yellow?). The second option is to make a separate type of stockpile that only auto fills. In both cases, since not everything can be made from the manager, only eligible items could set to auto fill.
How it works:
Every so often, the manager will do a check to see which stockpiles aren't full. How often can be set with a setting, like bookkeepers precision level. They'll figure out how many free spots are in the stockpile, and make equal amounts of the various items that goes in it. If its not specific enough, they'd do the next best thing, And if there's multiple options, they'd default to a standard one. For example, it would use "Brew Drink" if it needs Dwarven wine, or in the case of alloys, it would default to "make from bars" instead of ore.
Note, this would only queue up the orders, the manager would still have to go to his office and validate them.
Mechanics:
My current understanding is that empty stockpiles create a "move item here" job. This is pretty much the same thing, only if it fails, it now makes a "create item to move here" job. These would be created when the manager checks them.
Potential problems:
Game slowdown. By only having the manager check so often instead of constantly, it hopefully won't slow the game down too much
Ordering things made while already in the queue. If something can't be made because of lack of materials or time, it might be doubled up when it gets checked again. Easiest way to fix this would be to cancel all the non-player made orders with each new check. If it checks too fast there might not be enough time to make anything.
Stockpiles with multiple items. If a stockpile is for gold and silver bars, but your out of gold ore, it might keep trying to smelt gold instead of silver. Or if spaces open up one at a time, it keeps making gold instead of silver. Splitting up the jobs between all items in allowed in the stockpile should fix most of this. If the open spots are less than the number of items, adding them in a random order would stop the first one from being done more than the others.
Gems. There are a lot of gem types and the stockpiles don't let you pick certain types. I'd make it so only glass type gems work.
Bins/barrels and space. How to include bins into how much free space a stockpile has. I would have it only include bins that are currently on the stockpile. Using the max number of allowed bins might cause problems if there isn't enough bins for the stockpile after it gets filled. If you have extra bins, there's usually an empty one placed on each stockpile, which means more room during the next check.
Multiple materials. If something can be made from wood, rock, glass, and or metal, how would it pick which one to make it from. If it can be made from metal, which metal would it make it from. Or in the case of coke, would it use coal or lignite. Not sure how to fix these, for now I'd make everything default to stone. If it can't be made from stone, don't make it eligible. Things only made from one thing, like beds, would still work.
Multiple stockpiles or specific items. If two stockpiles accept the same thing, the auto fill one would fill them both up. Or if the stockpile only accepts a certain quality, or type of booze, it'd keep making them until it gets enough of the right type. Most of these are probably good things, and if you don't want them, changing settings should fix most of them. Like using the take from stockpile option to keep the auto filled one full before the others, or allow all qualities.
Uses:
Food: You'll always have x amount of prepared meals or booze on hand
Mandates: Someone wants 3 rings? Make a stockpile that only accepts rings that's 3 tiles big and doesn't allow bins. They'll keep making crafts until its filled, and then you'll have your 3 rings. (Might not get them done in time if it doesn't check often enough)
Production. Ammo stockpiles wont run out. With the exception of getting logs, using charcoal, pig iron, and steel bar stockpiles would automate your metal industry. A sandbag stockpile can help make glass. Have a certain amount of goods on hand for the next caravan while letting the worker do something else when you have enough.
Other
Not sure how long it should wait before trying to refill stockpiles again. I'm thinking the settings could be X times a month.
Maybe have the manager go to each stockpile before making orders. Not that important though
Involve the Bookkeeper somehow? Have him check the stockpiles, or make it go faster with good record keeping? Again, not that important
Anyway, I know there have been suggestions to auto-make food and booze, but when I searched I didn't see anything about using the manager or stockpiles.