Estimating calories for an event

Does anyone have any advice for estimating calories at an event like a birthday party? Especially when it’s at someone’s home and people are bringing dishes. For example, I can add an entry for a piece of cake, but I’m eyeballing that I got 3 tablespoons of mac and cheese, and the only way I can describe how much brisket I got is by saying 1 slice.

Would it be worth to guesstimate on each thing? Or have a catch-all meal that I list at like 700 calories or something?