The key to using simple objects for self-defense in public is to choose the right objects and use them in the appropriate way. Here are some objects and methods to consider: 1. **Key**: Hold the key and use the sharp end to stab the attacker's soft tissue (such as eyes, neck, abdomen). At the same time, stay alert and quickly escape the scene. 2. **Pen**: Use the pen to stab the attacker's eyes or other sensitive parts. Hold the pen firmly and apply force. 3. **Cellphone**: Use the cell phone to hit the attacker's head or body, which can be used as a barrier. You can also use the cell phone to call emergency services for help. 4. **Water bottle**: Hit the attacker with a plastic water bottle or spray water from the bottle to create a distraction and look for an opportunity to escape. 5. **Backpack or handbag**: Quickly swing the backpack to disrupt the attacker's vision or balance and create an opportunity to escape. 6. **Umbrella**: Open the umbrella to block the attacker's vision and stab the attacker with the umbrella handle. In any case, the first principle of self-defense is to avoid confrontation as much as possible and look for opportunities to escape or seek help. At the same time, understand local laws and regulations to ensure that your actions are legal. If your identity is compromised, call emergency services immediately.