General

Peanut butter and almond milk? Or any other milk than animal milk? Maybe nutella too.

I've just starting drinking gainer shakes and mine are basic, milk and double cream, plenty of calories per glass!

You can always check out the standard milk substitutes like Lactaid or Silk Almond Milk. I can honestly say I have no clue how well they'll work but those are the advertised milk substitutes.

Coconut Milk is the closest to milk texture wise according to google.