Although it’s mostly common sense, a few reminders are never a bad idea when it comes to safety. In general, if your scrapophone will be interactive, avoid glass and sharp edges. For example, while the saw blade shown here has some delightful sound qualities, it would not be such a good choice where small children are concerned.
The first thing to consider is your audience. If it is primarily adults you can probably use a few items you might want to exclude if your audience is mostly children. Also consider how interactive your scrapophone will be. For example, if it is primarily for performance where folks will just be watching, you can be more flexible in your choice of items.