A renewable resource is a resource that can be recreated indefinitely in survival without exploiting glitches (as opposed to a non-renewable resource). While running out of resources isn't likely to be a factor due to theoretically infinite (and still quite vast in practice) map generation, this is a list of resources that can be produced over and over without having to explore for more. However, running out of resources can be a bigger issue on superflat worlds, where resources are less plentiful, or in PvP maps, where one would like to obtain resources without having to conquer more land.
The listed fully renewable craftable items are items which can be crafted, smelted, or brewed using only renewable resources. For example, cookies are renewable as they only require wheat and cocoa beans that can be regrown infinitely, while TNT isn't because it requires sand, which is not renewable.
Anything that is dropped by a monster or animal, is renewable because more mobs of the same kind can spawn and be killed again for more loot. This is not the case for boss mobs (the Ender Dragon spawns only once per world, and the wither requires non renewable soul sand to spawn), nor the elder guardian, which spawns only three times per ocean monument.
There are some main methods to get renewable resources and some item-specific methods. Item-specific methods vary from building a cobblestone generator to harvesting obsidian from portals, so it's very important sometimes to choose non-renewable, but easier and/or safer ways to get them.
The methods are listed in increasing difficulty order:
Farming - grow it on the dirt or farmland block, breed using renewable resources etc.
Craft it using only renewable resource(s)
Buy it from villagers
Get it as a guaranteed or very probable drop after mob's death
Get it as a rare drop after mob's death
Find it while fishing
The first three methods are the easiest. They are especially worth using when you want to avoid risk, such as while playing in hardcore mode. The fourth method is normally used to get something that is only possible to get by killing monsters, such as blaze rods, arrows or bones. The last two methods are worth using only when there is no other practical choice, as you will really spend a lot of time executing the method before getting what you need.
These items are only occasionally dropped by monsters, so getting them quickly or in quantity is normally done by mining, then smelting/crafting non-renewable resources (mob farms being an option).
Bows are rarely dropped by skeletons, and can be enchanted with Power I and with an even more rare chance a Power II Bow followed by secondary enchantments. Usually, one would rather craft a bow with renewable sticks and string.
Can very, very rarely be found equipped to zombies, and skeletons. More commonly, diamond chestplates can be obtained by trading with villager blacksmiths.
Equipped items rarely dropped by zombies, skeletons, or zombie pigmen will rarely have enchantments on them (chance increases with difficulty).
Enchanted items may be traded from villager Smiths
Enchanted books are renewable by trading with Villagers and Anvils may be made from renewable iron, and many unenchanted items are renewable.
A single enchantment table can also be used indefinitely to create enchanted items from renewable items, experience, and Lapis Lazuli, but creating the table itself requires two non-renewable diamonds.
Sword is a rare drop of killed zombie pigmen. These swords can be enchanted with any level I and some level II or III sword enchantments. Armor can often be found equipped to zombies and skeletons.
Dropped only when a skeleton kills a creeper. It doesn't matter who dealt most of the damage, as long as the final blow is dealt by the arrow of the skeleton.
Obtained by trading renewable items to villagers, such as raw chicken. These can be used to buy other things from villagers, including resources that are otherwise non-renewable, like glass. Villagers never run out of stock (but their selling offers may vary), and they can be "bred", making villagers themselves renewable.
Obtained by trading with villager Librarians. Enchanted Books can also be caught when fishing. A single enchantment table can also be used indefinitely to create enchanted books from renewable books, experience, and Lapis Lazuli, but creating the table itself requires two non-renewable diamonds.
Obtained by trading with villager librarians. Glass bottles can be utilized to make potions. With redstone and glowstone bought from priests, extended potions and level II potions can also be brewed renewably. Glass bottles are also dropped by killed Witches.