You might be able to get a plain baked potato UNCUT at the restaurant. You should also bring some Lara bars or something similar that you can keep in your purse.
I don't know what your job situation is like but your boss really should accomadate your dietary needs. When you get to the restaurant and eat just a potato or nothing at all I'm sure people will ask. Then you can tell them why and I bet your boss will be shamed by these people you're meeting for not insisting on a restaurant you could actually eat at.