Home-brewers often use milk-based recipes — or literally just milk — to glue labels to bottles. Presumably it's the casein in the milk that allows this to work.
This kind of glue has the advantage that it's easy to make and use, and strong enough to stick reliably to bottles, but also doesn't leave residue when washed off with warm water.
Vegan gelatine substitutes are relatively easy to find, and agar would probably work for this, but what's a good substitute for the milk protein? Or alternatively, do you know of any commercial vegan glues that would have the desired properties?
I already make vegan beer, but it would be a shame to have to rely on animal products in the packaging!