I used to do periodic off-plan days to help shake things up, as anyone who's been around here awhile knows. It usually worked for me, BUT a lot of other people have tried it and had trouble getting back on plan.
If you do decide to try it, I'd recommend that at first you do it with low-carb foods - have some extra protein and fat, but don't add a bunch of carbs. That way you won't trigger cravings or get out of ketosis.
BTW, that's one reason the egg is a good idea, maybe better than an extra shake. Keeps your carbs low while adding some calories. And the extra fat usually helps in the sandbox, too.
Robin
203/130/130
Reached goal in August 2006
Added BodyBugg in May 2009
New ticker: 136.6/123.2/130