Here's my take on the subject as an educated layperson. Sorry, I don't have any cites handy, but I have done probably more than the average amount of reading on the subject. (And "reading" means articles printed in various technical journals.)
While not impossible, it seems to me very unlikely that any plausible EMP event will cause widespread destruction of individual electronic devices that are not connected to some sort of "antenna". This would include electronic ignitions and computers in most vehicles. The EMP itself does not cause any damage to electronics. What causes damage is voltages that are induced in conductors that are within the field. Generally, the conductor must be relatively long (in the order of a couple of feet or longer).
Most electronic devices that are just sitting on the shelf will not be damaged, because they are not connected to a sufficiently long "antenna". Undoubtedly, there will be exceptions, but IMHO, they will be quite rare.
Automobiles pose a special case, because they are large enough that they will have some internal wiring that will serve as an "antenna". Most of that wiring is somewhat shielded by the body of the vehicle, although it's not particularly well shielded. So there could be some damage to vehicles, although IMHO, it would still be relatively rare. Electronic ignitions would be relatively difficult to damage, IMHO. Computers would be more prone to damage. I suspect some will be rendered unusable, and a few might default into a "limp home" mode. But my guess (and this is just a guess, since we've never conducted an experiment of detonating a nuclear weapon in space above a populated area) is that most would survive.
That's the good news. The bad news is that the likelihood of damage to grid-connected devices is much more plausible, because they are connected to a long "antenna". So the TV that is plugged in to the wall at the moment of the EMP could quite possible be rendered unusable. Now, I'm not particularly concerned about my television, or anything else that is plugged in at my house. Even if all of those items are destroyed, I typically have spare versions of anything that I really need. Even if those spare devices are just sitting on the shelf, they should be fine, even if no special protective measures have been taken.
The real problem, though, is that the infrastructure (the power and communications grids) are very vulnerable. Let's assume that 10% of the electronic devices hooked to the grid are damaged. As a thought experiment, let's think about what would happen if we went around our respective neighborhoods and randomly destroyed 10% of the things that are hooked to the powerlines, telephone lines, Cable TV lines, etc. It seems to me that these systems would cease to function completely, and it would take extensive manpower and supplies to get them working again.
And if any needed supplies come from factories, then those factories are probably without power. So, in short, it's going to be a big mess.
The long and short of it is that all of your electronic devices (including your car) are probably going to be unscathed. Unfortunately, there won't be anything to plug them in to, and there certainly won't be any fuel available for the vehicle, since the refinery is also in the dark. And besides, I really can't think of too many good reasons to be driving around in a private vehicle in that situation.
Now, as far as the plausibility of such an attack, I really don't see any plausible way in which there would be a standalone EMP attack against the United States. Such an attack would require the detonation of a nuclear weapon on the edge of space, and would require that the weapon be delivered by rocket.
Currently, the countries that would be capable of doing this would be Russia, China, France, Britain, and maybe Israel, India, or Pakistan. If one of these countries did this, it would be a nuclear attack on the United States, and would certainly result in retaliation. It would make no sense for one of these countries to launch such an attack, if that was the only attack that was planned. They would be destroyed in the process, in exchange for conducting an attack by a method that has never been tested.
An EMP attack would be plausible, but only as one of the first shots of a general nuclear war. These countries all have enough nuclear weapons that they might possibly use one in such an untested attack, with most of them reserved for their more traditional purpose. So an EMP attack by any of these countries is almost certainly merely a predecessor to a general nuclear attack.
Now, let's assume that some new member joins the nuclear club. I suppose this could be Iran, North Korea, or a non-state group. At the present time, these countries have very few nuclear weapons. IMHO, it would make no sense for them to waste a weapon on an untested effect, when the other effects of nuclear weapons are so well known. There's really no good reason to go with an EMP attack, even if you had more certainty that it would work. Knocking out all of America's electronics isn't particularly any more spectacular than blowing up New York City. Since blowing up New York City is so much easier (and predictable in effects), that's really the most logical thing to do with your precious nuclear weapon.
Also, delivering the weapon is considerably easier if you use it in the traditional fashion. If you want to blow up a city, you can bring the weapon there by airplane, truck, boat, etc., etc. But for EMP, you really only have one choice, and that's to use a rocket. And even the best rockets sometimes blow up when you try to launch them. If you have 100 nuclear weapons, that's a risk you might be willing to take. But if you only have one, would you strap it to a rocket and hope for the best? Or would you put it on the back of a truck, knowing that trucks rarely blow up when you start them.
For those reasons, it seems to me quite certain that a standalone nuclear EMP event is exceedingly unlikely. If there is one, it will instead be the first shot of a general nuclear war. On the other hand, it might not be an apocolyptic war. But some other nukes would almost certainly be going off somewhere on American soil in pretty short order. Now, the United States is the country to have experience more nuclear explosions on its soil than any other country one earth, so this does not necessarily mean that it is the end of the world and that survival will be impossible. But the EMP itself will be basically just a footnote to the other things that are happening.
The long and short of it is that it would be embarassing to live through a nuclear war totally unscathed and then die a few months later due to starvation. So I think nuclear wars are things that one ought to give some thought for preparing for. Part of those preparations might include some electronic devices, and a method of powering them. If you want to be absolutely certain that those devices will survive, then it wouldn't hurt to seal them in a metal container. But IMHO, that's probably not necessary.
Now, a closely related subject would be some sort of solar event, such as happened in 1859. IMHO, the effects of such an event would be similar to an EMP attack--individual electronic equipment would weather the storm just fine, but the grid might be damaged to such an extent that it would be dark for months or years while replacement parts are manufactured. So giving some thought to planning for a very extended power outage is prudent, IMHO.