iOS/Mac: Copying and pasting between devices is a little tricky. If you don't want to rely on Wi-Fi, Scribe is a tool that does it over Bluetooth.
Unlike the previously mentioned Command-C which uses its own servers, Scribe sends all its communication over Bluetooth. This means that as long as your computer and your phone are near each other you can send information between them. Just hit Cmd+Shift+X and Scribe copies over text or images from your computer to iOS, or open the app on your iOS device to send data to your Mac. Scribe uses Bluetooth LE, so it's only compatible with newer devices, but if yours fit the bill, it works well. You'll need both the Mac app and the iOS app to use it.
Scribe ($2.99) [Mac App Store]
Scribe (Free) [iTunes App Store]