Get prohibitive dental work. My teeth are fucked from no fluoride in the water when I was a kid, so I always have more work needed.

Emigrate.

Shop around if you don't like your GP. Tell them your situation and ask them for a referal to every specialist under the sun. Get tested and innoculated for absolutely everything they suggest.

To your "edit" point: Don't take a handful of downvotes personally; it's pretty easy to do accidentally on mobile so they may have been unintentional

Colonoscopy!

Get all your injuries out of the way. Do a bunch of dumb shit to build character

Do every test available for prevention and prophylaxis.
Get your general practitioner to do a full health check, ECG, EEG, cardiac ultrasound, a full blood panel, bloodpressure, pulmonary function, skin cancer prevention ect.
Schedule a gastroscopy and colonoscopy.
Check in with an urologist to get your prostate and urinary tract checked.
If you can, get a full body scan. Either PET or MRI.

Nearly every serious disease or health issue is easier prevented or treated when caught before it casues real issues.
Every cancer there is, has a better outcome and is easier treated when found early. Most of them are silent until very late in the game.

This is something I would recommend to anyone: Take advantage of every preventative messure or examination that is available to you!
There is no illness that you can detect too early.

What you mean is, your HMO has had to dust off the "not medically necessary" stamp.

When this happened for me, I went and refilled my sumatriptan injections as fast as I could and actually used those for two years afterwards, it did save me money. If you need any extra dermatologist stuff, mental health, physical therapy, do it now.

Similar boat. Getting my snoring looked into. Got a sleep study done and now I'm having an ent do a scoping to see what's actually vibrating and what can be done.

Snip snip

Dentistry. This shit is always hard to get for free so you should do everything you can.

I say blow your free healthcare on something frivolous and fun.

See if they'll swap your left kidney with your right one.

Teeth. Teeth right the fuck now. And if somehow there is nothing wrong with them see if your insurance will cover a flouride coat to keep them that way.

Oh and literally every cancer screening possible. Get your butt checked, your nuts checked, some dermatologists will literally check every inch of your skin. Tell your doctor about every bad habit you have and see what else they're willing to look for.

If you're on any expensive meds, now'd be a good time to get them refilled. ...and 'my backpack got stolen!' them and get them refilled again if that's covered.

If you've got anything you think needs to be addressed with any urgency at all, skip the normal process and go to the ER to complain about your symptoms, especially if you've got ANY pain in your abdomen or tenderness in your lower back (which could mean kidney stones).

Infact, even if you don't have pain, go in and tell them you feel nauseous after eating anything greasy or fatty, and you'll get a free ultrasound of your gallbladder to see if there's any stones in there. ...don't actually accept surgery to remove it unless there are stones that look like they're for sure going to be problematic, cuz you WILL have symptoms once it's gone (eating will make you feel like shit... your body should adjust eventually, but that's not a guarantee, and it can take anywhere from a few months to years).

So, if they offer a scan or any diagnostic, do it. If they offer surgery, have a long think about whether it's actually worth doing.

Do you snore? Get a sleep study and a CPAP - thats pricy! Need a colonoscopy? Gel shots in your knees? Any family histories that would warrant testing for cancer markers?

This is the perfect opportunity to recreationally infect yourself with rare short term diseases. Try breaking your arm or nose so you have a story. Self harm has never been so cheap.

Edit: See evasive_chimpanzee's comment here, as the following seems to be incorrect information

Seriously though get checked for prostate cancer. Especially if you're over 25 it's very possible and catching it early will be a massive difference.

Same for everyone reading this. I doubt it's that expensive so please look into it and get checked if affordable where you are.