I'm not sure if this is the right forum to post this, but here goes:

When driving my AWD IS250 2008 in the icy winter season, I find that it has a tendency to skid alot, even with the 'SNOW PWR' option turned on. Because of this, I actually had my first car accident actually!

I'm guessing this may be because of how light the car is, and so I wonder if using stones or other heavy materials in the trunk would help at all by weighing down the car, and perhaps make it skid less?

I'm also thinking that because the car is an AWD, weighing down the car would not really make a difference, and would even make driving it worse by increasing fuel consumption? Does anyone have any experience or advice in this matter? Any help would be very much appreciated, so that when I get my car back from the dealers, I can feel more at ease! Thanks!

Three words for you:
Tires
Tires
and Tires

Check out the search features here and look for "Snow tires". There are some awesome threads recently from some knowledgable guys on the overwhelming benefit of the correct tires for snow/ice handling. They have suggestions on what to look for and which ones work best in certain situations.

Good Luck!

The one thing I would carry with me if I lived in an area with lots of ice is a package of roofing shingles from Depot or lowes. You can open up the package and lay them gravel-side down in front of each tire and get yourself enough traction to get past a bad spot.
I wouldnt carry stones; that might dent up the inside of your trunk. I have seen people here in Utah that put a couple bags of sand in the back of their rear-wheel drive cars and hope for the best.

Correct tires is the best solution however.

Do winter tires wear out a lot faster if driven on dry roads? I heard they are made from softer rubber so that they could move and push the snow out. I was considering winter tires at some point, but with New Jersey weather they would just be a waste of money since it only snows like 3 times during the whole winter season.

Yes, winter tires wear out faster than summer or all-season tires when driven on dry pavement. If driven only on snow, theoretically winter tires could last "forever" and would have to be retired due to age instead of wear. Also, more tread depth is needed for a winter tire to be truly effective -- at least 7/16 inch -- while a summer or all season tire can have as little as 2/32 or 3/32 of tread and still be usable in non-snow conditions.

We usually don't get much snow where I live either but I still use winter tires since we occasional drive a few hundred miles north where there can be a lot more snow. Plus winter tires take the stress out of driving in the few bad snows we get. Most other drivers are out there slipping and sliding around and I just zip right past them.

The way I make winter tires last longer is to wait until about Thanksgiving to install them and to remove them before the first day of Spring. At least once, I reinstalled the snow tires after getting a spring snow -- only takes me about 1/2 hour. The first thing I do when buying a rear wheel drive car of any make is to be an extra set of wheels to use with snow tires. For my first Lexus, I bought a set of "take-off" wheels from the Lexus dealer.

My current set of Bridgestone Blizzak snow tires are on their fifth winter and will be at about 25,000 miles and 6/32 inch of tread by the time winter is over. I plan to replace the Blizzaks at the end of the winter when tire seller cut their prices on winter tires.

Buying an extra set of wheels makes more sense if you keep cars a long time. We aim to keep cars a minium of ten years so that's spreading the cost of extra wheels over a long period of time. I've also found that having an extra set of wheels and snow tires makes a car easier to sell -- buyers seem to see them as a nice "bonus".