A stopwatch or watch of some sort to tell you how much time you're taking to get something done. 

A plan scribbled on a paper, notebook or a notes app to tell you what needs to be done for the day. 

A smartphone if you'd rather not wear a watch or carry a notebook. 

If you'd rather be guided on your routine, some device to show a video to guide you through the hour. And probably nudge you if you're taking it too easy. If you are in a gym with an actual coach doing their job or running a good session, you might just need a notebook to keep track of your progress. 

Next time you think a device, widget or tool is the missing link between your fitness goals and reality, just remember a lot more has been accomplished with a lot less than what you think you need to get something done. Maybe independence is just that realisation.