Quick math: In terms of total expected suffering averted, inviting a group of friends to a barbecue where the main meat is beef is probably more impactful than eating a vegan meal by yourself.

According to Faunalytics' Animal Product Impact Scales, a serving of chicken requires approximately 10 times as many days of animal life to produce as a serving of beef (not adjusted for quality of life or moral weights). Additionally, most seafood is much, much worse than this. If this meal prevents your friends from going and eating those other foods, tricking them into eating beef will likely do more good than eating a vegan meal by yourself. 

Still, this may not be as impactful as saving your money and donating it directly to impactful charities. Saving a single dollar on food and donating it to the SWP will probably do more to reduce suffering than hosting a barbecue. 

Also, you might expose yourself to various forms of value drift by hosting a barbecue, but I could see this happening in a net positive (hosting more barbecues in the future) or a net negative (giving up on veganism entirely/permanently failing to convince any of your friends to give up meat) direction.