The free ON1 Photo for Mobile app (currently only for iOS, vote for the Android version here) is a great way to take your photos with you. You can sync your favorite photos from your desktop computer to your iOS devices via Dropbox® or Google® Drive. Great for viewing photos, updating the ratings, keywords, and EXIF metadata. With two way sync, you can also send all the photos shot on your device back to your desktop computer automatically.
ON1 Photo for Mobile will be available in the Apple® App Store after the final release of Photo RAW 2018.