What happens if i have an accident with my rental car with no insurance?

You will typically be held liable - not a good idea. With no insurance, I highly recommend purchasing the Liability insurance supplement at a bare minimum from the company so if something happened you will not incur such a financial hardship. Not worth the risk in today's sue happy society. I also recommend the LDW or CDW coverage to avoid hassles such as upfront payments, inadequate coverage from credit cards (they are almost always secondary and never in full) and preventing the company suing you for damages.