You can currently read about this topic on the Squads Page.
- Picks allow your dwarves to mine.
- Battle axes allow your dwarves to chop down trees.
- Flasks allow your dwarves to carry water and alcohol. (Leather flasks are called waterskins, glass ones are called vials.)
- Backpacks allow your dwarves to carry rations.
- Quivers allow your dwarves to carry ammunition.
A pick is a foreign weapon that can be forged from most (not silver, for example) weapon-grade metals like copper and iron. Picks are required by miners to dig through the earth, carve staircases and everything else related to the removal of rock and soil tiles. You will need to supply picks on embark as miners won't bring their own. The material used when making a pick doesn't have any effect on its speed at digging through rock, that depends on the user's Mining skill level.
 Battle Axes
A battle axe is a native weapon that can be forged from weapon-grade metals like copper and iron. Battle axes are required by wood cutters to fell trees. You will need to supply battle axes on embark as wood cutters won't bring their own. The material used when making a battle axe doesn't have any effect on its wood-cutting performance; even wooden training axes are apparently capable of felling a tree.
Quivers are made of leather at a Leather works. Invaders, merchants, and migrants often have silk and cloth quivers, even though you can't make them yourself.
In adventurer mode, arrows and bolts picked up from the ground will automatically be placed in the first quiver worn, which can hold any amount of these ammo types. If filled with thecommand, it can hold up to an indeterminate limit of combined items. For examples: a quiver can hold 20 5lb raw or sharpened rocks, or 20 1lb bolts and arrows, but only two weapons or three articles of clothing of any combined weight.
In fortress mode, soldiers who are ordered to carry food (from the military menu) will equip a backpack to carry the rations in it, which saves them from going to a food stockpile whenever they are hungry. This does not mean that they will eat or drink while on duty, it only means that they will save time on their breaks. To prevent extreme hunger and thirst while dwarves are on an active schedule, you must lower the amount of soldiers required for a scheduled task, so that soldiers can be free to eat and drink.
Note that inactive squads will still carry food in their backpacks, and will eat it as civilian when hungry. You may wish to disable this, as while eating their rations saves on travel time, the dwarf will not receive any happy thoughts about their dining area.
Backpacks can be sewn from leather at the Leather works.
In adventurer mode, a backpack is required if you want to carry more than you can hold in your hands. Any items taken from the ground will be automatically placed in the first backpack worn (unless a quiver is worn, which receives any arrow or bolt,) with no limit to amount or weight. A backpack can be filled with the command up to limits too bizarre to be deciphered — just fill it by taking from the ground, okay?