Catering a small event tomorrow for twenty people. Serving beef brisket, pulled pork, and veggie lasagna. Question is how much brisket & pork should  allow for each person? also serving  three sides, rolls, etc.  
It depends in part who you are serving--hungry college students (or those with that mindset) eat considerably more free food than do wealthy health-conscious professionals.  You also need to keep in mind that while you don't want to overshoot massively, it also looks bad to run out of food.  You may also need to keep in mind that a significant number of people do not eat pork for personal/religious reasons, so you want to not run too short of other options.  That said, the best way to estimate is to see what people who do this all the time provide.  For instance, CityBBQ provides 8 lbs of meat for 20-24 people.  Famous Dave's seems to offer about 8 lbs also, if you can count their 60 chicken wings as equivalent to your lasagna.  (This is likely cooked weight, though neither site says.) 