Final answer:
At a picnic, a blanket is typically used to sit on because it is spacious and easy to carry, unlike chairs or tables, and a mat may be less ideal due to size constraints.
Step-by-step explanation:
For a picnic, an item commonly brought to sit on is a blanket. Blankets are often used because they are easy to spread out and can accommodate multiple people, making them ideal for picnic settings. Other options like chairs and tables can be more cumbersome to transport and set up, while a mat could be an alternative, though it might not provide as much space as a blanket. When planning a creative activity for a picnic, taking a large sheet of blank paper and various writing implements, such as pencils and pens of different colors, can allow for imaginative drawing or writing in an outdoor setting.