There are several built-in vehicles and signs in this mod. For many people, it's enough, but for some special users, such as servers, open saves, or realistic projects, it's usually not enough.

For solving this, MTR supports custom resource packs. Right now, it supports to add new vehicles and signs. Besides, you can also moderate something like decoration blocks in vanilla way.

Many of resource packs are packed in ZIP format. You can just put it into the .minecraft/resourcepacks folder, open the game, enable it, and use it like using builtins.

Some resource packs aren't packed in this format. For these cases, you should open the file and find if there are ZIP files in it. If you directly find pack.mcmeta in pack, you should decompress it into a folder in resourcepacks folder.

For other questions about using resourcepacks, see Minecraft Wiki for more information.

See Making a Resource Pack.

There are also additional mods that add new functionality (such as blocks or features) on top of MTR. They are installed like other mods in the same way as MTR mod.

For the list of addons, see MTR Addons.