I get off my "plan" for the day, too...but I do better than if I'd never made the plan at all.
As for exercise....there's a doctor in this state who started a website for bipolar depression. (I'm bp, too.) One of the suggestions I've clung to is tracking even 10 minutes a day of exercise--and counting it as exercise. Sometimes that's pulled me away from the beginning of depression, sometimes it's been the one thing I was able to do that day. Sometimes it's this long chart that I can be proud of....I hate it when I fall away from it, though, and look back at a past success and wonder why, why, why couldn't I maintain it.........That's when therapy returns to discussions of the Neverlasting and to methods of self-soothing--and of relying heavily on my support system, which often includes only him, because I am too ashamed to ask anyone else and am trying to hide how it is for me.
Now, it turns out, PC has become part of that support crew!