Hello
In my opinion I'm pretty good at putting grips onto bats, I've mastered the kwik grip and gripping cone. But when the grip won't suction for the KG of won't sit right on the handle from the cone there is a third method.
Yesterday I was coaching at a district match when one of my team came up to me and said he didn't have a grip on his bat. He was next in and getting desperate and then I remembered the plastic bag method. I managed to get the grip onto the bat quickly and efficiently, I was pretty impressed. I just tried it when putting a grip onto my new Kookaburra, again it was easy and the grip was place perfectly on the handle.
This is a very good technique to use if you are in an emergency or don't have a cone or KG around. I'm not sure how it would go with putting 1 grip on top of another, or doing it with a thick spiral grip but its pretty effective