[2020] How To Upload More Than One Than To The Workshop At A Time

I can't remember if there's a guide, but it's similar to how you would update. When uploading you click the little folder icon, which opens where the preview image is and where the file you're uploading is. Then you just copy in the other items you want to include in the pack and upload like normal.

https://steamcommunity.com/sharedfiles/filedetails/?id=424748932