A good quality multivitamin is always a good option. But if that’s not your thing; Omega-3, Vitamin C and Zinc.

I don't take vitamins and primarily eat meat

There is no universal answer that is right for everyone, it depends on your age, sun exposure, diet, exercise, etc.

Vitamin D3 is what most people should suplement. Omega 3, that is, fish oil, of also proven to be helpful for many things.

Check out examine.com

CoQ10 & PQQ

Only d3 when you don't get enough sunshine.

I take any letter of the alphabet I can get my hands on but definitely B-Complex, B12 (because I use metformin for life extension), C (not needed but why not), D, magnesium (sometimes), zinc (sometimes), DHEA, (no longer legal?) and cranberry extract.

I take daily dose of metformin for anti aging but these can cause a vitamin B12 deficiency so therefore I supplement B12 but would not take, or recommend taking, B12 when not taking metformin.

I usually get my vitamins in the Netherlands when I'm on leave because in Portugal, supplements come at a premium.

Metformin is only available on prescription in the Netherlands so get those OTC in Portugal. (cheap)