ItemTextureExporter is a simple utility mod that allows you to export all the items/blocks in the game the way they are rendered in inventory.
Modpack makers, mod authors, Wiki authors and all the other people interested in having exported texture data
Open the "Mod List Gui", and find Item Texture Exporter in it. Then select it. The "Config" button should now become clickable. Click it.
Now you can control the exporting process, namely the texture size - which is the size of the resulting image, and the export folder, which is the folder (relative to .minecraft), where the exported images will end up.
Then you click "Start export" and wait for the process to finish. Now you can find the resulting images in the folder specified above.
You can repeat this as often as you like, and it always renders the items in the texture the current resourcepack specifies.
If you want to add items with custom NBT to the export list (like for CustomModelData), or mark items as oversized because they clip out of the normal rendering canvas, you can use the "Configure" button to finely manage the export list.
This will present you with a list showing all items staged for exporting, as well as the associated NBT tag (if present). You can then mark it as oversized or delete it from the list.
Find the download here.
Although this project is licensed under LGPL 2.1, you (the user) are hereby granted a special exception: You may distribute the resulting images under terms of your choice, as long as you respect the copyright of the original texture creator. Usage of any of the images produced with this tool is subject to the license of the source images. I claim no ownership for images created with this tool. Use at your own risk.