If you are male and under 30 you should see a doctor every so often to get blood work done--say every 3-5 years. This is to check your blood sugar (diabetes) and establish a cholesterol baseline. If you're a drinker also start tracking your liver enzymes.
From 30 to 40 every other year is OK, unless you want to watch something more closely. If you're heavily involved in shooting sports and/or reloading, or some other sport with exposure to heavy metals or toxic chemicals discuss this with your physician and get the appopriate tests.
After 40 you're really better off getting blood work done annually.
As you hit your mid-40s getting your A1C baselined and then checked every so often is a good idea.
But yes, if you're paying out of pocket call around and see who will give you the best deal.
Also you really SHOULD consider a class of insurance (if you can find it anymore, idiot politicians have priced it out of some markets) called "catastrophic health care insurance". This doesn't cover you if you want an HIV test, or blood work, it doesn't cover your breast enlargements or vasectomy, but if an uninsured drunk car thief knocks you off your bicycle it WILL cover the bills he won't pay.
If you are male and under 30 you should see a doctor every so often to get blood work done--say every 3-5 years.
Pro tip: if you donate blood, they check it for free.
I am beginning to suspect that it is surprisingly common for intelligent, competent adults to somehow make it through the world for a few decades while missing some ordinary skill, like mailing a physical letter, folding a fitted sheet, depositing a check, or reading a bus schedule. Since these tasks are often presented atomically - or, worse, embedded implicitly into other instructions - and it is often possible to get around the need for them, this ignorance is not self-correcting. One can Google "how to deposit a check" and similar phrases, but the sorts of instructions that crop up are often misleading, rely on entangled and potentially similarly-deficient knowledge to be understandable, or are not so much instructions as they are tips and tricks and warnings for people who already know the basic procedure. Asking other people is more effective because they can respond to requests for clarification (and physically pointing at stuff is useful too), but embarrassing, since lacking these skills as an adult is stigmatized. (They are rarely even considered skills by people who have had them for a while.)
This seems like a bad situation. And - if I am correct and gaps like these are common - then it is something of a collective action problem to handle gap-filling without undue social drama. Supposedly, we're good at collective action problems, us rationalists, right? So I propose a thread for the purpose here, with the stipulation that all replies to gap announcements are to be constructive attempts at conveying the relevant procedural knowledge. No asking "how did you manage to be X years old without knowing that?" - if the gap-haver wishes to volunteer the information, that is fine, but asking is to be considered poor form.
(And yes, I have one. It's this: how in the world do people go about the supposedly atomic action of investing in the stock market? Here I am, sitting at my computer, and suppose I want a share of Apple - there isn't a button that says "Buy Our Stock" on their website. There goes my one idea. Where do I go and what do I do there?)