I am about to start a restaurant with my partner, and he will run the day-to-day operations.
However, if each of you is a 50 percent owner of the business, your salaries should be equal, unless you have a very clear understanding that the time investment each of you make is so disparate as to warrant a different salary. The reasoning is, if both of you are involved in the business full-time but you have different salary structures (especially if you forego a salary altogether), you could easily create a situation that breeds resentment.
Both roles--the outside face of the business and the back office functions--are necessary for the company to run smoothly. Look at the industry standard for determining the amount, but also see realistically what your business can bear. If it can't afford both of you at market rate, then both should take less.