This is a big update to CustomItems, which adds automatic resource pack generation for Minecraft versions 1.14 and up (older versions will be coming soon). This means that all you need to do is drop your texture images in a folder, and CustomItems will take care of making your resource pack for you!
After you add your textures to the CustomItems/textures folder (name them myCustomItemID.png), you can generate your resource pack with /cui rp gen
Check out the wiki page about Automatic Resource Pack Generation here:
https://github.com/jojodmo/CustomItems/wiki/Automatic-Resource-Pack-Generation