In Starfell: Willow Moss and the Forgotten Tale we meet the wizard, Holloway. Who sails the Great Melee and owns a bathtub-boat called The Sudsfarer. He has learnt to make food almost seemingly from air – stuck as he is sometimes for ages out at sea. When he makes food he uses whatever he has at hand. Including rain water for flavour!
Using your own store-cupboards, why not have a go at making your own rain biscuits?