My suggestion would be to let yourself have some of the cake, some of the pizza, etc-- then go out for a little extra exercise this evening, eat just a little less tomorrow (if it will make you feel better), then just go on with your plan as usual. One day of over-indulgence won't make a difference in the long haul as long as you don't let it mean more than it really does.
I've written this before but I think it still applies- when we were gaining the weight we didn't eat badly and fail to exercise
every day. We managed to eat the odd salad here, and go for a walk there. But because we maintained an unhealthy lifestyle, those good days didn't impede our gain. Now that we are maintaining healthy lifestyles, a bad day here and there shouldn't impede our loss.
Skinny, healthy people eat cake and pizza too, just not as often as we used to.