I put together hundreds of kids projects a year, whether for elementary school or VBS. The way to keep these projects clean and orderly is to put them in zip lock bags. Little or no passing out is required!
Then you have to go through making the project in your head so you don't forget anything. Like right now, looking at this picture, I know I need to get scissors out. I'll put this stuff into a bigger bag and set it aside knowing that I'm ready for day 1. Tomorrow I'll deal with day 2!