Hotbox's. What to get.

The first thing I suggest you do is find out what the HD, in the areas you plan to serve in, allows. Depending on the venue you may be required to prepare your food(s) in a licensed kitchen and there may be items that you are not allowed to sell on site.

For festivals we cook onsite and serve as product is finished.

For catering we use Cambro S-Series carriers.
LINK
Size will depend on the amount of product you need but the above link will help determine what you may need. If available check locally to see if you can rent this type of item since they are not cheap. We purchased since we do not have a rental option near us. They can run around $400 new.

Check this thread for good info on how much pans will hold.
http://www.bbq-brethren.com/forum/showthread.php?t=160565

We tried using condiment cups for individual BBQ sauce serving once (I emphasize we only did this ONCE). It was a nightmare filling them all and trying to keep up with more when we ran low/out. We put bottles out (in an iced container for HD regs reasons) and just figure that cost in with the overall price of the items we are selling.

For catering we do provide paper plates (heavy duty Chinet brand) and plastic silverware (good quality clear utensils from SAM's since the cheap ones break too easily). Again this is calculated into our over all sales pricing.

For festivals/farmers markets we use Dart foam hinged lid containers for sammies and Dart foam 6 oz deli containers w/lids for sides. We have found that paper plates are not good for festivals/farmers markets due to the wind factor (it is very windy at times in KS :shocked. Peeps like to have the ability to cover up their food if needed and the cost difference is negligible.