I passed by the university town today and accosted a girl.
Your answer is obviously wrong. Sister said this, but she was actually asking you out. You should say: shopping alone is boring. I will accompany you, and then you can help her make up her mind, or give her some advice when shopping. Then you can help bring things down, buy some water when you are thirsty, and find a place to sit down and rest when you are tired. Let's have some crayfish and beer tonight. ...