As a long-term nutrition science enthusiast, I warmly recommend the following supplements regardless of your diet and lifestyle. While it is technically possible to get these things through diet, for most of us it's highly impractical or too expensive.

Vitamin B12: the safest, most reliable way to get B12 is through supplements, 1000mcg a couple of times a week is sufficient for most people. You might not have had an issue with this yet because our bodies store B12 for a long time, but as someone who wound up deficient (long before I went plant-based) I can testify that you don't want this to happen to you.

Vitamin D3: there's a lot of misinformation out there, lots of doctors recommend actual sunshine but for most people it's unlikely to be sufficient and also carries the risk of skin cancer. You'll also find that most medical literature is concerned with "deficiency" but not "insufficiency", and this hormone has a dramatic effect on overall health. The officially recommended amounts are not in sync with what researchers have determined, which is that we should all be ingesting 2000-4000IU on a daily basis.

Omega 3: we all know omega 3 is important for brain function, what most people aren't aware of is that sea-based sources now include such high mercury payloads that you're more likely harming your brain than helping it with fish-based supplements - especially true for the developing brains of children. Fortunately, milled/ground flax seed (not whole, those aren't really digested properly) are a great source of omega 3s (two tablespoons per day should suffice), and there are plenty of other plant-based supplements now available.