Ladyrider, we all fall off plan sometimes. The most important thing, I believe, is to accept it, and get right back on track with your food & exercise plan. If you don't like protein shakes, don't drink them. Just get right back to your normal eating & activity habits. The most "extra" I do when I slip up is to try and drink lots of extra water to flush out any water retention, and I make extra sure I get to the gym b/c for me, a good workout keeps me really motivated.
I doubt you gained 8 lbs in one weekend. More likely you're retaining water from the off-plan foods and alcohol. Getting back to on-plan eating, workouts, and lots of water as I mentioned above should help flush out the extra fluids.
As to the psychology behind a slip-up... not sure how much your question is about that as well. I do try to figure out why I had trouble, so I can prevent it in the future (this doesn't always help me, but it does sometimes). e.g. Was I emotionally eating b/c I was lonely/bored b/c I had a Friday night home alone? Make plans with some friends next Friday...that kind of thing.
Don't beat yourself up too much. It happens to everyone. Just get back on track. You're doing great, you've come so far, keep up the good work!
