Thank you for sharing your dream. It sounds like a complex and vivid experience with several themes at play. Let's break it down:

1. The Sandwich and Rat Poison: The imagery of the sandwich and the rat poison might represent feelings of anxiety or fear about something that seems appealing but could be harmful. This could reflect concerns about a situation in your waking life that appears safe or enjoyable but has hidden dangers. The fact that your boyfriend realized the mistake before consuming it suggests a desire to protect loved ones from potential harm.
2. Cockroaches: Cockroaches often symbolize feelings of disgust or anxiety, and their presence in your dream alongside the ruined sandwich may indicate feelings of being overwhelmed by negative emotions or situations in your life. It could also point to something that you perceive as unpleasant or undesirable being exposed.
3. The Empty and Crowded Streets: The transition from emptiness to overcrowding can represent changes in your life or emotions. The empty streets might signify a sense of isolation or feeling lost, while the crowded streets could symbolize overwhelming challenges or distractions in your waking life. This shift can indicate your feelings about navigating through different phases or emotions.
4. The Carrier: The two-legged carrier you mentioned could represent your need for support or a means to transport your burdens or responsibilities. The fact that it wasn’t yours may suggest feelings of borrowing or relying on others for help, or it might indicate a desire to take ownership of something that is not fully yours at the moment.
5. Searching for the Carrier: Your quest to find the lost carrier amidst the chaos could reflect feelings of searching for stability or clarity in your life. The uncertainty of the streets being empty again might indicate a fear of losing direction or control.

Overall, your dream seems to explore themes of anxiety, responsibility, and the search for stability amid chaos. It may be beneficial to reflect on any current situations in your life that evoke similar feelings and consider how you can navigate them more effectively. You might want to communicate openly with your boyfriend about any fears or concerns you have, as this can help strengthen your relationship and alleviate anxieties.