Yep a bottle of wine would do the job. Since it is a barbecue, you could give a bottle of nice barbecue sauce. You could give a small potted live house plant. I agree with you that you want a gift that creates zero work for the hostess. You could also do a nice tea towel.
This sounds like fun! I can imagine that you are going to be nervous since you have been out of the social loop. Just go in remembering what a wonderful person you are. Relax and enjoy, don't try to hard. Just be yourself and have a great time!!!