If you are sued due to an auto accident, anything over the limits of your automobile policy will come directly out of your pocket, and potentially your future earnings. You will want to carry liability insurance limits high enough to protect assets like your home and 401(k) plan.
The recommended limits for most people are $100,000 per person and $300,000 per occurrence. If you have a home that is more expensive and have built up your retirement plan, you may want to carry higher limits and look into getting a personal umbrella policy as well.