Presentations such as these rely on a reflection of your work at the internship, while incorporating humor to ease the tension.
Focus on the work you performed for the presentation, but also include interactions during the internship that were exciting and fun (so that the internship wasn't just any other job).
Throughout the presentation, try to add some humor, whether it be engineering-related jokes (or comics), inside jokes that those around would understand (something like: "..and when so and so says to get that finished by the end of the week, it usually means by the end of the day, ha ha ha..."), or reflect on something funny that happened. It's these interjections in a presentation that separates itself from the boring ones we are all used to.
Since this is an informal presentation, this can be a more relaxed atmosphere, but still in line with presenting information. Good luck!