Get a Empty Bottle before you go into the next dungeon with few hearts. You can take healing with you instead of having to make up for every misstep until you reach the next teleport stone. In normal story mode there are three bottles: one on the beach and two in hidden merchant caves. Their position on the world map depends on your game status.
The bottle at the beach vendor
Find the merchant in the beach hut on the coast. His bottle costs 80 Rupees. If possible, buy them on your first visit if you have enough money. This is a more sensible early purchase than temporary equipment that you have to replace after a failed attempt. Still missing Rupees, explore neighboring unvisited fields and open accessible chests before visiting the hut again.
The two bottles in Beedle’s stores
The remaining bottles are in two hidden shops. Examine cracked walls on the rocks and grassland areas and place a Bomb on the suspicious section. Step back from the explosion and go through the resulting opening. In each of the two Beedle shops in question you can get a bottle for four diamonds. They are two different businesses; a repeated visit to the same store does not replace the search for the second one.
If your map already shows the cave symbols, go through the merchant markers specifically. Otherwise, the cracked walls will help as a local clue. When restocking your supplies, also check the shops you passed early in the adventure: Bombs or diamonds could have been missing back then, even though the entrance was already accessible.
Pack healing and refill used bottles
With an empty bottle you can buy a red healing potion. It replenishes your health and is also triggered when you lose all hearts. A green potion, on the other hand, restores stamina. When buying, pay attention to what help you need for the journey ahead: If you get a lot of hits, healing will be more useful to you than additional stamina for special attacks.
A fee can also be taken along as security. After consumption, the bottle remains intact and can be refilled. Therefore, check the contents before entering a boss chamber. Especially on the way through Hyrule Castle and the future it is worth going back to the dealer as soon as the last healing reserve has been used up.