Extras
Make sure not to forget the special calming blankets or stuffed animals or other toys that helps your child stay under control. Museums are new different anxiety inducing places. Make sure that you have the spacific toolds that help your child stay comfortable.
Technology
If it is a longer trip make sure to plan for the car ride. Often Special Needs kids need something to hold their focus to tame any brewing tantrums. The care can often be extreamly overstimulating and can make Sensory and other kids feel overwhelmed and trapped in a kind of wind tunnel. Ipads, movies, and car bingo are all great car ride activities.
Snacks
Snacks will almost always save a difficult moment while goig through the museum. Always have a filling snack such as beef jerky or fiber granola bars. We also carry a juice box or other drink for each child. I make sure to ask when we arrive if there is a good place about half way where the snack can be eaten. NEVER EVER leave the house with out a healthy filling snack and drink. It WILL save the day at some point.