To make a hay sack, use an empty sack on a searchable hay bale or use it on any haystack present. You may then use a bronze spear on the hay sack to create a hay sack (spear), and a watermelon to make a scarecrow.
To fill your sack, you can go to:
- The "inner" Barbarian Outpost (Agility training course)
- You can also fill sacks from hay bales: north of Draynor Village, north-west of Lumbridge, and north of Ardougne.