Potions are effectively extra max health in lane phase. At level 1, most Champions have between 500-600 health, and just one Health Potion restores 150 health. Not having that sustain against someone who does really adds up in trades, and this is true throughout lane phase. Also, having that sustain lets you stay in lane longer for more farm; if a Health Potion lets you stay for just 3 more CS, you've more than paid it off.
The Refillable Potion is good for Champs who want to sustain efficiently. Supports, for example, want to stay on the map longer to control vision, make plays, etc., without spending their limited funds on Health Potions. ADCs, on the other hand, can use the Refillable Potion's sustain to farm more and easily pay it off, instead of struggling to pay off more and more Health Potions.
Generally, if you're getting more Health Potions on first back, and think you may buy even two more later, get a Refillable Potion instead. It costs as much as 3 Health Potions (150g) and is worth more after just one refill. You effectively have 250 more health for as long as you carry it, and it sells for 60g, meaning you only lose 90g for having bought it - chump change past lane phase.
A second Doran's item is situationally good - excluding Doran's Shield, which you almost never want to buy in the first place. If you're forced to back early without enough gold for a meaningful item purchase, getting a second Doran's item will give you the health, damage stats, and sustain to lane more efficiently and either close the gap with your opponent or increase your own lead. You lose about 250g for each Doran's item you sell later, but that's negligible past lane phase, and isn't worth near as much as a CS lead or getting/denying first blood.