There are few things that can put the missing piece to the puzzle like taking a throat sample. When done properly it does not harm the fish, and you can get an exact reading on what the fish are choosing to eat on that given day. Throat sampling is essentially drawing up what the fish has recently eaten, and you can expect most of the bugs to still be alive.
Super, super nerdy. I mean, I really try to tell as few people as possible that I like to force fish to regurgitate the bugs they ate for lunch, so that I can put them in a glass vial and take photos of them with a macro lens. However, this does allow you to get a perfect idea of what can be created at the tying bench.