Resource Packs
Resource Pack Download
You can automatically get the server resource pack by using the command /rp in-game. Make sure you are playing on the latest version (1.12.X is recommended) and have the server resource pack on "Enabled".
If that does not seem to be working for you, you can try to install the server resource pack manually. Below, you can find how you can do that. Before the tutorial starts, make sure you have disabled the server resource pack.
Tutorial
Step 1: Use the command /rp while and you will get a three different download links in chat. No you can open the link to download the resource pack. Make sure you open the right link so you download the right resource pack for your version (1.9-1.10.2 / 1.11-12.2 / 1.13+).
Download resourcepack for 1.13+
https://pack.grandtheftmc.net/1.13
Download resourcepack for 1.11 - 1.12.2
https://pack.grandtheftmc.net/1.11
Download resourcepack for 1.9-1 - 1.10.2
1.9-1 - 1.10.2: https://pack.grandtheftmc.net/1.10
Step 2: Open the link, it will bring you to a website where you can download the resource pack. Do not open this file!
Step 3: Go back to your Minecraft, click on Escape -> Options -> Resource Packs.
Then move to Resource Packs...
Step 4: From there, you can click on "Open Resource Pack Folder". Your Minecraft resource pack folder will open.
Step 5: Drag the file you got from Step 2 inside the Minecraft resource pack folder you just opened.
Step 6: Go back to your Minecraft and select the resource pack you just installed.
That is it, now you should have the Grand Theft Minecart resource pack.