Skip the supplement aisle. Apples, cabbage, and a small handful of walnuts cover a surprising amount.
Apples are close to a synonym for good health — potassium, magnesium, calcium, iron, pectin, and vitamins A, B, C and P. Even the seeds are useful: a couple a day help top up iodine, which many people run low on.
White cabbage is the underrated everyday vegetable: low-calorie and rich in beta-carotene, vitamins C, U and B, and potassium. About 200 g of raw cabbage covers your daily vitamin C — just remember that boiling destroys it, while fermenting and juicing keep it.
When it's cold, your body burns extra energy to stay warm, so heartier, warm meals are fine in moderation. Walnuts are excellent — five kernels give roughly a day's vitamin C plus minerals and protein — but they're calorie-dense (~650 kcal per 100 g), so keep it to 2–3 a day.
A quick cheat-sheet for where the vitamins live: vegetable oil and walnuts for E, carrots for A, wholegrain bread, buckwheat, oats, rice, cauliflower and beans for the B group, and pomegranate for C.