What besides milk can I use in my smoothies?

I finally got my own blender, and I was planning on drinking smoothies every day to gain weight, but I live with 6 relatives, and my sister who also makes smoothies does not want me to waste the milk, so I can't make smoothies every day. I cant buy my own, and I don't know what else to use. Is there any thing I can use as a replacement? ( when i say i can't use milk, almond milk/ alternative milk also applies.)