Start the game with 6 Minion Dematerializers. Killing minions with the item gives permanent bonus damage vs. that minion type.
+5 Armor or 6 MR (match-up)
WhyGrasp of the Undying
Grasp on Poppy allows her to trade incredibly well in lane and sustain a ton of damage thanks to her massive resist stacking. The heal and bonus health from Grasp make every point of health much stronger due to those resists.
Demolish is a fantastic rune choice for snowball early gank kills for a quick team gold lead.
Conditioning's duo resist buff at 10mins synergizes well with the additional resists from [W] making you incredibly tanky and resilient in the mid-game.
Poppy's biggest pitfall is her lack of mobility. She can be a threat to squishy champions if she is able to stick to them. Unflinching's Tenacity/Slow Resist allows you to dive the backline and stick to them for kill threat.
Magical Footwear's raw gold value is huge for hitting your crucial mid-game 2 item power-spike.
Minion Dematerializer is great for empowering your ability to shove the lane at match top laner roams during jungle skirmishes.