It can be a challenge doing what you describe and I have been doing it for a number of years. I just did ribs, pulled pork and Dutch's beans for 120 last weekend. Pulled pork I always do a week or two in advance at home. I vac seal and freeze it and rewarm at the event site. Ribs I prep the day or two before. Remove them from the cryovac peel the membrane and do whatever trimming is required. Rewrap in food service wrap and refridgerate until it's time to transport to event site.
Some of the items I have acquired over time that are needed are pop up canopy. Get the biggest you can with a vented top. Mines 13X13 and has the vented top which allows the smoke and heat to escape while keeping you and your smoker out of the rain. I will say I have been darn lucky over the years with the weather.
A 3 bay propane steam table.to keep things warm for as long as you need while serving at the site. Expensive but worth it's weight and then some. Big Johns makes them. Portable and built solid. I tried roasting pans but they draw way to much electricity. 15 amps most of them. Each! Most places I go to have a garage or 3 season house they set the serving line up in and they won't have enough power to run more than 1 roasting pan. I tried chafing pans with the sterno fuel. Big pain in the butt! They really don't keep things that warm and you have to constantly monitor the fuel to see if the flame went out or if it's to for a new fuel can. With the steam table I have no worries. I just take a 20lb propane tank and I can go all weekend with it and set it up anywhere!.
For food transport I use coolers. I freeze empty juice bottles full of water. Put them in the bottom of the cooler and put the food on top. They take a lot of cooler room but they will keep your food cold enough overnight even and your food won't be floating in water like it does if you use just bags of ice. You will need several coolers on hand.
The last time I left the pulled pork frozen solid in the bags and used them in place of frozen water bottles to keep the ribs cold. Worked great. I kept them in the cooler like that overnight and when I opened the coolers the next morning to start prepping some of the ribs actually started to refreeze. I just left the pulled pork out until it started to thaw enough to break up and then threw it in the steam table to start to heat through.
Get yourself various sized restaurant pans they are invaluable and saves cost on all those aluminum foil pans. Buy 18" wide X 500 yard rolls of aluminum foil and food service wrap and butcher paper and buy dispensers for each.
I also have a couple of Cambria food keepers. These are awesome to keep things warm or cold.
Those 4 and 6 foot tables that fold in half are great and transport well. There is more. Always keep a pen and paper at hand. When you are going about your business of prep work and cooking you will always find yourself saying I should get one of (fill in the blank) don't try to remember it write it down.
Craigslist is your friend if you have the time to wait to accumulate things.
I have trailer rigs I can strap stuff down to is how I transport a lot of this stuff. I have a motor home I trailer the smoker with to the event site most of the time. Often times I'm on site the night before setting things up. I usually wind up joining the festivities after all the food serving and clean up is all done. Should I enjoy one too many cocktails the motor home is a nice crash pad
Yes, I have spent Friday to Sunday at some of my events but it's always a good time and get paid to boot!