Preventive services are the part of the system most likely to be free and least likely to be used.

Many preventive services — screenings, vaccinations, routine checks — are covered without charge under most arrangements. People skip them anyway, generally because they expect a bill to appear afterwards.
Recommended screenings depend on age, sex and family history, and the list changes. Asking a clinician which ones apply to you specifically takes a minute and is more reliable than any general list, including this page.
Diabetes and high blood pressure cause most of their damage quietly over years. Regular, boring monitoring is what prevents the expensive emergency later, and it is the first thing dropped when life gets difficult.
Both are commonly treated as optional extras and both have substantial effects on general health, nutrition and the ability to work. Community programmes for them exist in many places and are advertised almost nowhere.
Screening for depression and anxiety is a standard preventive service in most systems, and asking for it is ordinary rather than exceptional. Delay here is common and costly.
Nobody holds a complete picture of your care — records sit with whichever provider created them. A single page listing what was done and when, kept by you, prevents repeated tests and missed follow-ups more reliably than any system.