Floki gathers some mushrooms which he personally gives to Rollo, still recovering from his injuries, and has Ragnar's son Ubbe give some to Torstein.

What food did Floki give Rollo?

Being a good friend and good host, he offered his find to everyone, including Torstein. Rollo offered Torstein mushrooms as a form of pain relief, which I suppose could go to his favor as he was trying to aid his friend in the only way he knew of at the time?

Did Floki heal Rollo?

Horik was then forced to walk across the great hall while Ragnar's supporters each took a turn at the fallen king until Ragnar brutally finished him off — using just his head! So, Horik's dead, Floki's back to being a good guy (so much so that he even helped heal Rollo) and Ragnar is the king.