Most teams won't be vending until later - they don't have time. A lot of vended food is NOT cooked on-site - it's brought in. Temps had an influence on a lot of teams - I got to Winter Haven about 8:30 and did a walk-around.
Some events have concession people come in - but they do the snowcones and that kind of stuff. Some do a variation on grilled stuff - some events you must compete to vend and some let anyone pay to vend (Plant City is like that - snowcones, funnel cakes, etc. :D
After about noon a lot of teams start selling the "left overs" from the competition stuff. Others, like Buttrub.com bring enough staff that they start vending earlier. Prices vary but tend to be around $1.50-$2 for a rib and about $4 or so for a pulled pork sandwich. Chicken and brisket are hard to find unless you schmooze and beg a bit!
To get the stuff that actually is entered you need to schmooze :D Find a team that seems friendly and hand around and watch. Stay out of the way during the turn-in windows but if you ask questions and look hungry you'll often get to taste whatever just went to the judges.
The other option is get judge's training and start judging! :D At FBA and most KCBS events find the judging area (no, you can't observe!) and shortly after the last (brisket) turn-in the judges are released. Find one that looks like he/she won't bite your head off and start asking questions. Often they (we) go out to the teams for a taste of what they sent in (it's blind judging so we don't know who's food we judged) and see how they felt the event went for them.
This is when you can look at the cookers and ask questions. The beers are opened and most teams will talk while they cleanup.