Siphon is a Limited Time Mode solo game-mode in Fortnite: Battle Royale and the second daily LTM game-mode. It was released on December 20, 2018 and was removed the next day. In the game mode, you do not get any consumables to heal with. The only way to gain health is to kill a player, and 50 health or shields will automatically add to your health.
However, the community made posts on reddit about consumable heals in Vending Machines.