I fashioned a wooden surface/portable desk for my car that sits tilted. I am wondering what can I cover it with so electronics like phones and tablets can sit on it inclined and not slide off. What comes to mind are padding stickers for furniture? Is there anything better? Surface is around 10 inches sq.
I would get some self adhesive Velcro strips and stick a few pieces on the electronics with the other side on the wooden shelf.
This is how I used to keep my clip board secure on my dash, it was aluminum with a space for my basic contracts so it was kind of heavy,
it stayed in place. I put the soft loop side on the clip board and the strips with the hooks on the dash and that way the clipboard was not trying to stick to anything but my dash (I first had it the other way with the hooks on the clip board and it would try to stick to some clothing).
Most quality devices, like my laptop have non-slip feet already. BUT, if you have a steep angle or the inertia forces are too great they won't hold.
I keep my devices, like my 15" laptop in a protective shell and it is in a padded bag when in the car, so even heavy braking will not cause an issue.
As mentioned in comments, you can get grippy plastic mats for phones/pads etc.
They are properly 'sticky' but it's not an adhesive, it's a property of the very soft, rubbery plastic. They get dusty over time & need a rinse in the sink to restore full adhesion.
They are remarkably sticky & adhesion improves over time if a device is left in place. The smoother the surface the better the adhesion, of course, but they'll stick to just about anything.
Back in the days before I had built-in CarPlay, this would stick my phone to the dash day in, day out.
I did a quick demo video [too big to upload directly here] slapping one onto the vertical front of some wooden utility drawers, then two tries at sticking an old iPhone to it & pulling off again - first with a gentle push, second with a more firm twist & push. It would stay there all day if left alone. The drawers are not actually flat to each other, so the phone is really only stuck to the top half of the pad.
I found an ad online, where they reckon you can keep your phone safe even barely touching a curved surface - maybe so, but I wouldn't like to test this precarious mount over rough ground…
Click for full size