Callum, the evidence-based list for a symptom-free 31 year old is short enough to be almost disappointing. Blood pressure is the single highest-value check at your age: raised pressure is common (roughly 1 in 3 adults aged 30 to 79 worldwide), silent, and takes under a minute to find. Beyond that: a cholesterol panel periodically, typically every 4 to 6 years if you're low risk, sooner and more often with a family history of early heart disease; blood glucose if you carry risk factors rather than as a default; sexual health screening, which is at its most relevant in exactly this decade; and for women, cervical screening from the mid-20s. Add an honest conversation about smoking, alcohol, weight and family history, and that is genuinely most of what the evidence supports at 31. The site's guide to screening in your 20s and 30s walks through each of these and why the list is short.
Now the other side of your dad's menu. Resting ECGs, tumour marker panels and broad ultrasounds in symptom-free young adults are not recommended by the major evidence bodies, and it isn't because they never find anything. It's because of what they find: incidental results of uncertain meaning, which arrive far more often than early disease does at your age, and each one buys follow-up testing, not health. Annika's six weeks is the typical purchase. Screening programmes start at the ages they do because that's when a condition becomes common enough for testing to help more than it misleads. A 31 year old and a 58 year old getting identical "recommended" packages is a statement about the clinic's checkout page, not about medicine.
The caveat that matters: family history can genuinely move items onto your list early, as Gregor says. So the best use of your allowance might be the least glamorous one, a blood pressure check, the basic risk-based bloods, and an unhurried conversation with your own clinician about what your particular history brings forward. What I can't do from here is know that history, which is exactly why the checkout page shouldn't decide this either.