The best ones are the skill level one since most of the kids are at that phase. Models keep the kids busy. They learn about all kinds of things from building models, from reading plans to aircraft components. Actually any kind of wood or plastic model would be great, cars, boats, ships, the visible body, airplanes, etc. Airplane Tee shirts and hats would be a big plus.
Kids love to wear tee-shirts, new or used, the airplane message is important.
Used Airplane maps. Kids like to look at maps, really any kind of maps and globes are a plus. Airplane toys are great for the younger kids. Airplane toys keep the kids dreaming and keep them learning about technology. Toys for little kids and toys for bigger kids are needed.