I believe that if you can stack up small victories all day long, you create discipline (saying no to refined sugars, sugary drinks, and fast food) and develop resiliency in building solid habit loops. I like doing 10 pushups at the top of each minute over 10 - 20 minutes several times per day.
Each hour try to do a set (or more) of 5 or 100 pushups depending on your fitness level. It will help you start looking at your days differently. While you may not have 1 full hour to dedicate to the gym, you DO have 1-3 minutes each hour over the course of several hours throughout the day.