Autumn sq'irkjuice is made from Autumn sq'irks, found in the Sorceress's Garden minigame. To make the juice, pick 3 Autumn Sq'irks (requires 45 thieving) and use them with a pestle and mortar, gaining 5 Cooking exp. You must have 3 Autumn Sq'irks and a beer glass in your inventory in order to make the juice. In the Autumn Sq'irk garden, you will also find a Herb bush that allows you to pick two herbs at a time.
Picking the Autumn Sq'irk will give 50 Farming experience. Drinking the Autumn Sq'irk juice will restore 15% of your energy and give you a Thieving bonus of +2, although it is not recommended to drink it as you can give the Autumn Sq'irk Juice to Osman for 2,350 Thieving experience.