About a substance called Sugru
Sugru is a highly useful and fun substance, sort of a combination of moldable rubber and glue. Amazingly it sticks to virtually any surface with chemical glue, including smooth metal or plastic.
It makes many repairs and fun ideas much easier to make. It's not cheap and it takes a day to cure, but it's still worth it. For example I have made grips for a couple of tablets and a camera, and they really help. (Sugru is not very grippy, sadly, so I had to invent a way to put grainyness in. Dabbling the surface with a toothbrush before it dries works pretty well though.)
There is a wealth of ideas on their site. Here is their newsletter.
Below is a grip I made with super-grippy surface. You can also see a strap I put on the tablet case with superglue. I think the strap is even better than a grip, actually, but they are both much better than nothing. I am amazed that four years after iPad One there are still almost no solutions for improving the grip on a tablet, and those that are there demands the whole hand behind the tablet, you can't have the thumb in front to change pages. With mine you can, making one-handed reading much more comfortable.
I cut the front of the case, since when folded back it gets in the way of the strap and grip. You can also put them directly on the device, I've done that with my Kindle Fire HDX.