The pre-ride question gets answered in two parts: what you eat the day before, and what you eat the morning of. The night before, you don't need anything elaborate — a normal carb-led dinner (rice, pasta, potato with protein and veg) is enough for a ride up to about 4 hours. Above that, slightly increase carb intake the day before, but the dramatic 'carb-loading' protocols you read about apply mostly to marathons and full-distance triathlons, not most sportives.
The morning of is where most amateurs underdo it. The current evidence-based target is 2-3g of carbs per kg of bodyweight, eaten 2-3 hours before the start. For a 70kg rider, that's 140-210g of carbs — a substantial breakfast. Porridge with banana, honey, and a scoop of protein hits about 90g; add toast with jam and a piece of fruit and you're at the right number. Coffee is fine and helpful. Fat and fibre should both stay low to avoid GI distress.
30-60 minutes before the start, take a smaller top-up — 20-40g of fast-acting carbs. A gel, a banana, a small bowl of cereal. This sits on top of the earlier breakfast, primes blood sugar, and means you start the ride with full glycogen and no insulin crash. Dr David Dunne and the Roadman race-day nutrition guide both walk through this two-meal protocol in detail.
What to avoid: anything new on ride day. Anything high-fat or high-fibre within 4 hours of the start. Sweetened coffees with cream. Large amounts of dairy if your gut isn't used to it. The pre-ride meal is not a tasting menu — it's a fuelling intervention. Pick a breakfast that's worked in training and use it. Race day is the wrong time to discover that overnight oats with chia don't agree with you.