Quickdraw is a glitch which allows you to instantly start holding an item without needing the pull-out animation. It is useful for situations that need you to quickly use an item after holding an object. One example use for it is performing the Cucco Jump to Gerudo Fortress as Child with a Deku Stick. The two methods of performing Quickdraw are canceling the pull item animation with water or shielding damage, usually from explosives.
Jump in water and pull out an item (either a sword or a Deku stick) just as Link hits the water. The next time Link uses that item it will appear in his hand without playing the unsheathing animation.
It is used in this video to cucco jump with a Deku Stick, which is not normally possible.
A much more prominent use for Quickdraw is Duplicating a Bottle over your Sword
By pressing B on while shielding a damage source that has a multiple-frame hitbox, or by shielding damage from two damage sources in succession, you can cancel the drawing of the sword. This causes Quickdraw to occur when you next pull the sword. More interestingly, this also sets the "last button used" value to your B button, while still keeping the previous item you were holding in your hands. This allows you to Shield Swipe over the sword for Bottle B. A bomb or bombchu is generally used due to its availability. As an adult, there is one frame to press B and you must be in front of wall to get Quickdraw. As a child, there are multiple frames to press B and you do not need to be near a wall, so it is considerably easier.
As an adult:
As a child:
Action swap is a glitch which an extension of Quickdraw. If you have an item in your hand, then quickdraw another item, then use the item you quickdrew, you can get some interesting effects.
If you have a first-person item (Bow/Hookshot/Slingshot/Boomerang) in your hand, then quickdraw a Sword or Hammer, then use that item twice, you will shoot an arrow or deku seed, depending on which age you are. Note that you need to have an arrow or deku seed in order to shoot them.
If you have a first-person item in your hand, then quickdraw a deku stick as adult, then use the deku stick twice, you will shoot a flaming arrow.
If you have a first-person item in your hand, then quickdraw a deku stick, then use the deku stick to draw it, then light it on a torch, you will get an extremely long upside deku stick.
There are various other effects you can get such as playing wasteland sound effects or using the boomerang as a sword.