How many onboard toys can you put in an SUV?

I must return the wireless headphones. They belong to the 2005 Jeep Grand Cherokee Limited sport utility vehicle we drove to New York over the Thanksgiving weekend.

I removed the headphones from the SUV because they are considered “personal items.” No one who values property leaves personal items in a vehicle parked in a big-city garage.

The rear-seat video screen, six-disc dash-mounted CD player with MP3 capability and the optional Sirius satellite radio system are also personal items. But they are fastened to the Grand Cherokee and, anyway, there are only so many personal items a person can carry from a vehicle to prevent theft.

That’s a problem. At least, that’s what I’m thinking, looking at the two sets of headphones sitting on my home-office desk. Cars and trucks nowadays come with so much stuff. They are rolling living rooms, bedrooms and family rooms. At a post-Thanksgiving rest stop on the New Jersey Turnpike, we used the Grand Cherokee’s huge center console as a table and turned the vehicle’s interior into a restaurant.

We ate and ran -- fast.

Please understand: We were not speeding or showing off. Other motorists were zipping past us in everything from little Mini Coopers to giant 18-wheelers. We allowed them to do that. Going 70 miles per hour in a 65-mph zone is one thing. Going 90 on a crowded post-holiday highway dampened by rain is insane.

We’re not crazy. But the people at Jeep, an arm of DaimlerChrysler AG’s Chrysler Group, may have gone a bit bonkers. They’ve put a Hemi in the Grand Cherokee Limited. Yep. Along with the DVD and MP3 player, satellite radio and satellite navigation system, leather seats and numerous other luxuries that have not much to do with driving, Jeep has added a 5.7-liter, 325-horsepower Hemi V-8 engine capable of developing a humongous 370 foot-pounds of torque.

In a vehicle as big and boldly styled as the new Grand Cherokee, that kind of power, generated by a surprisingly vibration-free engine, could seduce and corrupt the gentlest of souls.

On many occasions, we were creeping along so slowly that only four of the cylinders in the Grand Cherokee’s Hemi V-8 were active. That’s because the big engine is the progeny of odd-couple engineering. It uses the Chrysler Group’s new Multi-Displacement System technology.

MDS employs a series of sensors to detect speed and load. In traffic jams when nothing is moving, or when the vehicle is moving at a snail’s pace, four of the eight cylinders are electronically deactivated to save fuel.

MDS-type technology will be offered by a variety of light-truck makers in the near future. General Motors Corp., for example, uses a similar system, which GM calls “displacement on demand” in several of its large pickups.

Frankly, I’d like to see more of that kind of useful technology going into more cars and trucks, as opposed to the increasing level of gimcrackery that has nothing to do with the on-road performance.

I mean, really, how many video screens, DVD and MP3 players, remote headphones, hands-free communication devices and mobile Internet portals do we need? Are all of those things freeing us to enjoy the road, or are they forcing us to worry about which component or device will be missing if we are unfortunate enough to park in the wrong place?

I could have sworn that the garage attendant on East 53rd Street in New York was salivating when we pulled up in the elegantly rugged, device-laden Grand Cherokee Limited. “That’s a nice truck,” he said. “We’ll watch out for it. Don’t worry. We’ll take care of it for you.”

Said my wife: “That’s going to cost us a big tip.”