As you start adding more Android apps and games to your Chromebook, you're going to need to occasionally manage files like a real Android device. The built-in Chrome OS file manager is woefully inadequate. The best Android file manager I've ever come across is Solid Explorer, and it works wonderfully on Chrome OS. This app has a dual-pane interface for easy navigation, drag and drop functionality, creating/opening ZIPs, and fast indexed searches. It's easy to get around the interface with a mouse, and it's great for touchscreens as well. This app has a free week trial, and after that it's $1.99 to buy.
Solid Explorer (free trial, $1.99 full version)