Power Banks:
Any lights or sounds that you add to a costume will require some sort of power. The easiest way we have found to run these items is with cell phone power banks. Their prices have really come down and they are easy to recharge and will usually last for hours running these costumes. 

LED Lights:
There are a variety of light choices out there and are always changing. These LED strip lights are great because they typically come with a remote to allow the child to make them whatever color they want. Just make sure you buy lights that are powered by USB so you can use them with your power banks. 

Bicycle Wheel Lights:
If you search for anything "wheelchair" related (cup holders, lights, etc.) you'll find they are extremely expensive. However, if you search for the same items but for a bicycle, the price drops significantly and are often the exact same item. These lights for wheels on bicycles are great for the big wheels on a wheelchair and can really add some punch to the costume. And as a bonus, the child can keep them on long after they don't wear their costume. These are also sold at Walmart and Target.

Sound Effects Buttons:
​Depending on the child's disabilities, they may not have fine motor skills, pressing little buttons, or pulling triggers could be difficult for them. Using large buttons that are programmable are much easier to hit with your palm, or fist.  

Tap Lights:
One of the easiest ways we have found to make headlights and tail lights is with tap lights. These are usually run with 2-3 AA or AAA batteries and some even come with a remote for the child to turn them on and off. Tap lights that only turn white can be used easily for headlights, while tap lights that at least offer a color change can make great red tail lights.