If there is more than one adult or older child in the car, having someone to sit beside him is a huge help.He really should still be backward facing. I am big on allowing electronics in the car, even for toddlers though Im pretty strongly against them in general for toddlers. movies or apps on a ipad are great. Tons of snacks, a few books and small toys. I like the crayola products. The color wonder markers are great and we like the magic dough. No mess at all and the kids love creating things in the car with it.
For the trip its self, think simple. His clothes are tiny, so take plenty but keep them simple and matchable as much as possible. Good footwear is important if you think he will walk much. Take a good, lightweight stroller with a good shade. A hat and sunglasses, and extra sippy cups. Good safe sunscreen. A lightweight bag for the parks. I liked the small light weight fabric backpacks when mine were little and it can hang on the back of the stroller. Take any medication for him you could possibly need. Are his parents going too? Have an emergany plan in place and consider a notarized consent to treat letter if not. We take a virus care kit. Yes we did learn the hard way on this one. Extra PJs, paper towels, plastic bags, cleaners, drinks and simple easy foods like crackers. I also like a few simple toys for the room for any down time....a few cars or invest in the huge mr.potato head box from DDT on the first day. Our little guy played with this the entire trip one year. Think through where he will sleep and take any sleep friend or pillow. Avoid any big changes like taking passy or bottle too close to the trip. It will be fun and really not to hard ......enjoy.