Actually, you want them angry, then. Angry elves bring rare and exotic animals. Happy elves bring cloth you could mass-produce yourself. It might effect your wood count a little bit, too, though. Personally, I keep 'em upset by offering them a wooden bin after trading them all the mugs out of it.
This is not true anymore. It was true in 40d, but in 31.x this changed. Happy merchants try to bring more of everything, but load up binned materials first. In 40d, elves who were very pleased with you would want to bring so much binned cloth that their pack animals wouldn't have any weight capacity left to carry anything else. In 31.01 and beyond, in order to compensate for the currently-nonfunctional wagons, all pack animals had their weight capacities increased, and all items were made significantly lighter-weight. As such, elves no longer fill their animals' packs entirely with cloth, and will bring more of everything, including useful exotic animals, the happier they are with you.
Can I ask a question about food production?
Doesn't making roasts INCREASE the amount of barrels you need?
I ask this because ill often see a few small things like, 1hunk of meat1bit of beer and soem surger, used to make like 300 roasts or something. Doesn't this mean you need MORE barrels if you are making extra "advanced" meals?
No, because roast stacks that have 11 or more roasts in them don't use barrels at all. If you had, say, 8 dog meat, 3 dwarven sugar, some bear brains, and 15 quarry bush leaves, that would take 4 barrels. Cook those 4 ingredients into a roast, though, and you get 27 quarry bush leaf roasts that take 1 square of storage and won't be put into a barrel, and even once 17 of those roasts are eaten the stack will still take only 1 barrel.