The short answer is that it's inconsequential either way. The long answer is that the traffic code actually does carve out a decent number of exemptions, and parking anywhere is probably one of them although it's been a while since I skimmed through -- but they're always with a caveat that it's for reasons related to actual work, so personal errands don't count. Food would be a gray area because it's a necessity more than a luxury in some sense, and theoretically time spent on legal parking would be time that could be spent on actual duties.