The reason Bobby's bag was very heavy:
- The text states that the previous evening, Bobby had collected all the necessary things for his trip.
- A list of these items is provided: a warm pullover, two pairs of socks, football boots, a ball, his favourite cap, a box of chess, badminton rackets, a T-shirt, a book about adventures, a pencil case, a note, a camera, sunglasses, an umbrella, a sleeping bag and a tent.
- Additionally, his granny was putting some snack in it for him, specifically cheese and ham sandwiches, a bottle of water, some hot tea and sweets.
- The sheer quantity and variety of these items, from clothing and sporting equipment to books and food, would naturally make the bag very heavy.
Answer: Bobby's bag was very heavy because he had packed many items for his trip, including clothes, sports equipment, books, and snacks.