Lots of answers, and only 1 talked about which sanctioning body. Not all competitions, not all sanctioned competitions, are the same. Some have multiple turn-ins which can require more meat, and in some MUCH more meat because of the other styles of judging. That said, it does sound like you're referencing either KCBS or FBA, I'll guess FBA as you're in Florida.
In FBA you'll generally fill the box with meat, usually a little more or a lot more than you would in KCBS, with KCBS's garnish allowance... That could require you to cook a *little* more. For example, in KCBS many get away with 6 1-bone slices on their bed of greenery. That same 6 pieces wont work for FBA; you're more likely to have between 8 to 12 in there...
I tend to fill my KCBS box like I would my FBA box, so for me I cook the same, but you'll see it's a little more than most above.
I usually cook 4 butts, because I want 2 money muscles and I want 2 butts cooked to perfection. We cook 2 briskets because I push them very close to over-done, and hopefully at least 1 will be perfect. 4 racks of ribs, mainly because we like eating the leftovers here. I could do with 3 racks... 16-20 chicken thighs, for us, has always been PLENTY. I will tell you I've seen Bub-Ba-Q (as seen on BBQ Pitmasters) come out of their trailor, trip, and dump their entire chicken box in the sand. Luckily they had enough made so that he went back inside, wiped the box, put another 6 or 9 thighs in there without garnish and ended up 2nd in chicken and GC'd the competition.
Hance - Lake Dogs Cooking Team - MiM/MBN/GBA CBJ and comp cook
Lake Sinclair, GA (strategically about an hour from darn near anywhere)
Started competing in chili cookoffs back in the 1990's and have competed in more than I care to count. I became a CBJ in MiM in 2005, then MBN and in GBA in 2010. I've probably judged 130+- BBQ comps (sanctioned and unsanctioned) over this time. That said, I really enjoy competing more than I enjoy judging, and hope to get back to doing 4 or 5 a year in the near future.