"Prevention > Cure" and "investment in you and the things you use most will pay dividends in terms of health, money, and mobility" is the very TL;DR version.
If you're in a country with an asinine healthcare system like the US, it's definitely prudent to take care of your health rather than being caught out by something. This includes regular dental check-ups and cleaning (trust me).
You spend a lot of time sleeping. A good mattress and linens are very valuable to your health.
If you are on your feet a lot, comfortable should also be a priority even if they cost more.
Work out to your ability. Being sedentary is detrimental to your health and causes pain (both physical and financial).
Try to save and buy better quality versions of things where it makes sense. If you only spend $10 on something but it lasts only a year, it's better to spend $30 or $50 on something that lasts you ten years or a lifetime.
Remember that investments can take many forms and pay out differently. Investing in your health is already mentioned, but invest in your education. If you don't have money, you can still find tons of free resources online or at the library to skill up in ways that help your life (either your job prospects, your home life, or even your mental well-being).
And, perhaps more importantly than most other advise, live within your means.
I realize that not all of these are possible to everyone all the time (I was homeless for a while; I understand). These are goals and any progress is worth it; do not let perfect be the enemy of good.