Teamfight Tactics has a number of good items for this purpose. But three of them really shine in the early game while still remaining useful later on.
B.F. Sword + Chain Vest = Guardian Angel. This item revives the defeated champion wearing it with 500 health. This gives your uber-champion more mileage, almost doubling their durability in the early game when most enemy champions will be 1- and 2-stars.
Recurve Bow + Needlessly Large Rod = Ginsoo’s Rageblade. Each attack grants 3 percent attack speed, stacking infinitely. A self-explanatory item, it is unstoppable early on when enemy champions can’t easily chain-stun, banish, or otherwise stop you yet. The Rageblade is particularly powerful on a number of tier 1 champions, including meta-favorite Kassadin.
Recurve Bow + Tear of the Goddess = Statikk Shiv. Every third attack deals 100 spell damage in an area around the target. This item hits really hard in the early game, and can still be useful later on as the board crowds up.