Sometimes, people have life problems that can be entirely solved by doing one thing. (doing X made my life 0.1% better, PERMANENTLY!) These are not things like "This TAP made me exercise more frequently", but rather like "moving my scale into my doorway made me weigh myself more, causing me to exercise more frequently" - a one-shot solution that makes a reasonable amount of progress in solving a problem.
I've found that I've had a couple of life problems that I couldn't solve because I didn't know what the solution was, not because it was hard to solve - once I thought of the solution, implementation was not that difficult. I'm looking to collect various one-shot solutions to problems to expand my solution space, as well as potentially find solutions to problems that I didn't realize I had.
Please only put one problem-solution pair per answer.
A pull-up bar: cost $10, installation in door frame 5 minutes, allows me to do pull-ups spontaneously at any moment. Which sometimes leads to other forms of exercise.
Then a small problem appeared, because I installed the pull-up bar in the bedroom door (reasoning: this door is used least frequently, so people would be least bothered by having the bar there), but it turned out that no one minds the bar, however I cannot exercise when other people sleep. Solved by installing another pull-up bar in a different door frame.
A stepper: now I can exercise while watching movies.