I would rethink the kids camera. We did the research and bought one for DS before our trip when he was 5 and it just was a disappointment. They are all too big to carry around and they are sometimes more difficult to manipulate than a regular one. I would buy a very basic, inexpensive but trusted name brand regular camera for him. Same or less money and it will grow with him and hopefully be less frustrating.
Other ideas:
A mid-size rolling duffel bag in a pattern he can use for a while. We travel a lot and we got DS one in camouflage that he will be good for quite a few years rather than a kiddie print he will out grow soon. Also bought a size he can grow with for a while.
Consider a gaming system IF you are ready for him to have one and you have a longish trip. We bought the leap-pad system at four and it was not a good investment for us. He wanted a DS and we were not ready for him to have that yet. He had no interest in the leap-pad and it went unused till be broke down a bit later and got the DS. It is an awesome travel tool and because we restrict use at home, that unlimited travel time play is great. There are games for 4-5 year old but that is about the youngest I would consider. Another idea is an itune card so he can help choose a few new apps for your pad or iphone. If you REALLY want to spurge.....I was good with my little guy having an ipad at that age and they are GREAT travel tools.
Other travel toys: Magnetic scene toys, etch-a sketch, magna-doodles, color wonder.
A new Car Seat- We are huge car seat safety people and 4 is about time kids start to our grow some of the convertible seats. I love the 5 point harness booster that hold 65+ lb kids. If you are driving......so worth the investment.
Happy Planning!