Minecraft wiki entry for Superflat_survival, associated text: Lava and obsidian cannot be acquired in this challenge, making the Nether inaccessible. Also, you cannot make a cobblestone generator, which means no furnace and no smelting. However, there are other ways to obtain stone tools and cooked food.
Expect frequent deaths, because obtaining any equipment requires a lot of time and patience.
If you play on Java Edition, then it is recommended to play on 1.14.2, as later versions have removed the spawning of vindicators (only source of emeralds) during patrols.