Getting married next month. Not sure what financial steps we should take

Marrying my longtime girlfriend next month and we're planning to combine finances. We have similar salaries, savings, spending habits, and debt (none besides our mortgage), so it should be seamless. Still, some questions I have are:

• What do we do about credit cards? Keep using separate ones? Add the other as an authorized user? Apply for new ones jointly?

• What about retirement accounts? Are there such things as "joint" IRAs or 401ks?

• Do we open new joint bank accounts?

• Is there any reason to be on the same health insurance plans if we both receive it separately from our employers?