Hmm... eating pure protein shouldn't take you out of ketosis, but the damage you might do to your frame of mind by introducing food could be something you'll end up regretting...
Once people come off plan, they often find it very hard to get back in the zone... And subsequent 'picking' on this diet just becomes harder and harder to resist... and could lead to ultimate failure. I know you may think 'pah, I'll be fine, I'll get right back on plan after'... but read a few of the diary's on here, you'll see it can be a real struggle for some...
I'd really encourage you to reconsider your decision to eat... If possible...
I went to a wedding a month ago, and I didn't eat anything. I had my shaker in the car, and went out before the meal and made myself a quick shake, drank it, then went back in... no-one was any the wiser.
And, when people asked why I wasn't eating at the meal, I said I was on anti-biotics and they made me feel a little queasy if I ate on them... was also the perfect excuse as to why I wasn't drinking alcohol too!
If you plan to be on an abstionence diet, then that's what it is. Complete abstinence from food. No if's or but's...
/my 2p worth...
xx