I have always take some meat to a BBQ....however i have never just eaten what i take... (i know in my social circle) that we all through it in and share!! And i take my own eski with my beer in it! If ppl want a beer....! And if its my house i'll provide fridge space and an ice bucket.
As regards to money.... What goes around comes around.....you have your barbie, invite all, give them a good night, then when they have one they invite you! All works out pretty similar for all then!