Nothing really new, nonetheless I share the technique I used to make a new grip head to my keys.
Many of you already know Sugru, the silicone-like material to fix things and make nice rubber parts. Since it's a very resistant material you can add a thin layer around your key heads and make them coloured and rubbery.
Step 1: Modeling
After opening your sugru pack divide the sugru in small parts, depending on the number of keys you want to cover. Usually with a single Sugru pack you can cover three normal keys. Clean with alcohol the keys surface.
Divide again each part in two and place two halves on opposite sides You can both push a Sugru ball on the surface, or mold the Sugru in a cylinder and place it around the hole. I prefer this last method, since in the first case you then have to open the hole and move the paste away. Help yourself with a pen to open and keep clean the hole, then clean all the edges, push Sugru with you fingers on all the surface, especially on the edge.
I used a piece of cloth to imprint a texture on the paste surface. Here is where you can make your keys very characteristic. Depending on the fabric or the object you use, key's head will be more or less unique.
Step 2: Imprint the texture
Place the key between two layers of cloth and gently press for about ten seconds, no need to push hard. Then take out the key and check there are no imperfections. You can make the process again if you wish, second pass will cover the first one.
Place the key on a support and let it rest for about two or three hours. I did it stupidly before having to go out, and it was very funny since there is no way to close the door avoiding to ruin your new grip before at least one hour...