Twos are fun travelers...everything is new and exciting. Six hours really in not that long of trip. If possible, I would leave about four hours before nap time (assuming he will sleep in the car. Drive 1/2 way and stop for a meal at a fast food place that has a good play area that is safe for a toddler. Let him play while you eat and then give him his food as soon as you get back in the car. As soon as he is done eating, turn off any noise, put up any toys, and give him any nap time comfort objects and he may well sleep the second half of the trip and wake up happy. First three hours should not be too hard.....a few toys, a movie or two and sing and talk to him.
Once you arrive....think through your activities. Will you spend most of your time on the beach and in the pool? Bring lots of bathing suits and simple shorts and tanks that can get wet and sandy. Think about shoes...
crocs are great!! Think about time on the beach,: toys, sun screeen, sun glasses, shade umbrella, beach towels, cooler for snacks. Will you go out for dinner or other activities?....an outfit for each night at least +1 or2 extra. Sandals or crocs. Think though bath time.....tooth brush his paste, soap etc. PJ's + and extra pair. His pillow and blanket if he uses one. I always took a good amount of my boys favorite toys on beach trips as we needed and wanted some down time in our condo. I would hide a few things for a couple weeks before the trips and then they seemed almost new again. I would take match box cars, legos, action figures etc. Always took tons of books, mostly paper backs to make lighter bags. Take sippy cups, plenty of wipes, diaper needs and extra diaper rash cream, even if trained. Kids tend to get chaffed at the beach. Take baby powder in your beach bag and sprinkle on sandy kids to help get the sand off. Take plenty of drinks and snacks for him, even if you don't plan to cook any.
Remember that toddlers on the beach are soooo fun but require constant supervision, frequent sun screen applications and reminders to drink. Take tons of pictures and make wonderful memories.