FAQ
Minecraft: Default Pack
Disclaimer: Use these packs as REFERENCE, don't put your models inside them, it just increases your pack needlessly. Also don't put any of the unedited files from it into your own pack. The distribution of default assets in your pack is illegal.
For Java Edition:
Simple Method
Use the Pack Creator utility from the Resource Pack Utilities Blockbench plugin. Make sure to enable the Import vanilla assets option.
Manual Method
(This works the same for all versions, 1.21 is just used as an example here)
Go to .minecraft/versions/1.21 and open the 1.21.jar file with a zip program.
Alternativley you can copy the .jar file and change the file extension to .zip, then double click it.
Extract/copy the "assets" folder from inside the jar. This folder contains all the default models and textures.
For Bedrock Edition:
Go to the bedrock resource pack documentation and scroll to "Building the Resource Pack". The download for the vanilla resource pack can be found right above that title. You can also use this Direct download link.