Why It's Important: Mainly, you want to make sure your car's heating and defrosting units are working properly in addition to everything else, and you also might want to consider snow tires which will make drives a little less slippery. There are also a ton of great hacks out there for scraping ice and not letting your locks get frozen. The Cost Of Not Doing It: You don't want to deal with a car that's literally too cool to start, and the snow can cause you to drift a bit more than you want to. Proper car care throughout the whole year will make sure you're ready for whatever comes.
Why It's Important: Not only do car mats provide cushion and relieve your feet from heat, they also keep dust and water from causing an absolute mess in your ride. Investing in quality, easy to clean mats like the ones made by OxGord help ensure that you aren't bringing anything into your car you don't want. The Cost of Not Doing It: Letting stuff like sand, water, and dust fall onto your car's interior is probably going to cost you a lot of time in cleaning, and can have some unintended effects on your car if left long enough. 5 minutes cleaning a mat or an hour cleaning your car's carpet, your choice.
Why It's Important: Letting your car roast under a hot sun can cause some unwanted heat damage to your interior and paint job. Find a nice tree and park under it, and if there isn't a tree, buy a nice sun shade to stop the burn. The Cost Of Not Doing It: In addition to causing interior damage, UV rays from the sun can melt plastics, crack your dashboard, and cause fading on your paint job. It also isn't the most pleasant thing to sit in a scorching hot car, so for the sake of you and your butt, find some shade.