Stealth
Leaf
Stealth is the foundation of most speedrun categories that go beyond act two. The FRW, FCR, and FHR bonuses are enough to guarantee finishing your run with a faster time.
Likewise, Leaf is essential to any fire builds that run beyond act two. The idea is that with RNG permitted, you'll find these runes roughly around the same time that you find Stealth's.
You also benefit from the great experience that the Forgotten Tower offers with your multiple coutness runs.
Javelins
Dagger Or Scimitar
If your main attack is too weak, Javelins will annihilate most things in early Act I. Extremely useful for The Countess when running with assassins.
If running with an assassin, your trap/fire blast speed is based off your weapon on hand. Daggers and Scimitars are the fastest weapons to easily acquire at Act I
FHR Gear
Getting FHR lock is a bitch. While you're at Charsi, quickly skim over any items for sale with Faster Hit Recovery. Don't do this until you have money though. They usually cost around 1,000 Gold.
Potions
Stocking on stamina and mana potions as soon as possible is essential for a good run.
Antidote potions will make help you tank Andarial & Mephisto. (+50% poison resist for 30 seconds)
Thawing potions will help you tank Durial & Mephisto & Baal. (+50% cold resist for 30 seconds)
Ral'd Helm
Tanking in Act III - V can be challenging with little to no fire resistance. If you find any extra Ral runes during your countess runs, throw them in a 2os helm to tank those infernos much better. If you don't fnd any, then shop for FHR Gear, but keep in mind that a Ral rune may drop sometime during your run! Also 3x Tals can transmute into a Ral.
FCR/Skill Wands + Staves
Generally speaking, I've found that getting + skills weapons at the very beginning is more beneficial than getting FCR weapons. Of course getting an item drop with both would be ideal, but it will not happen often, so you'll need to shop for a weapon. You'll need to have a good amount of gold saved up before you start shopping since these weapons are expensive, usually ~3000 - 8000 gold.
With shopping RNG considered, I usually buy the most reasonable item that I first stumble upon. I wouldn't want to waste too much time resetting the shop for a specific item (such as an FCR weapon) if there's an affordable +skills weapon that I can get, and vice versa.
Gas potions are useful for difficult to kill mobs and very large groups of enemies. Just throwing one is quick and will deal a lot of damage. Throwing a few at the countess and her minions could save you time if your primary skills don't deal a good amount of damage yet.
Charms
Sell junk charms for gold. Ideal charms to keep have a good amount of life and resistance. If you find a good charm early on, it may be worth selling it if you still cannot afford your mana and stamina potions.