I think this should be the last thing from your mind. You are under 200 and will not stand out as fat. Be proud of who you are. Try to focus on protein and low carb veggies. I would take some protein bars and keep them for when you need something healthy in case it is not available.
Most potential inlaws will want to know about who you are and your family. They may want to know about your education, upbringing, your family, religion beliefs, your talents and interests. They may also want to know about what you love about your significant other and what makes your relationship special. Hope this helps...I look forward to hearing how it went. Also, everyone loves a house guest that is considerate and helpful