I have used Aleene's tacky glue to glue items to a wall hanging, but if the item is too heavy it may not hold up over time. For a coin could you use invisible thread and tack it on by hand? I have used glitter in a wall hanging and just used regular glitter that I bought at Michaels. I think it was Martha stewart brand in a kit kind of thing. Aleene's works well for sequins and "jewels". My personal preference is to avoid glue guns.....I just make a mess with them.