Some extra information about this texture pack merger.
Itsme64's texture pack merger is an increadibly simple tool that allows users to merger as many texture packs together as the want online, by simply uploading them straight to the website and clicking on the green Merge button!
The merger selects the pack with the lowest index and chooses it as the base pack. Then it adds every other pack onto the existing pack (sorted by index) without overriding any of the existing textures.
Resource packs made with this maker will by default always support the latest Minecraft version. If you want to change the version your texture pack works for, then visit the version converter.