From Thursday (T-3) lunch through Saturday (T-1) dinner, target 8–10 g of carbohydrate per kilogram of bodyweight per day. For a 70 kg athlete that's 560–700 g of carbs daily — roughly double a normal high-carb day.
What works: rice, pasta, bread, potatoes, oats, bananas, white pasta with low-fat sauce, sports drinks, pretzels. What doesn't: heavy fats (cream sauces, fried food), high fibre (large salads, beans), spicy or unfamiliar foods, alcohol.
Expected: 1–2 kg weight gain by Saturday night, mostly water bound to stored glycogen. This is normal and good. Don't panic at the scale on race morning.