Different venues have different things on offer, so the chances are you will have to see what is available and choose on the day.
I don't drink alcohol, and find that there is a huge variation from places offering a wide range of non-alcoholic 'grown up' drinks to those where the best you can hope for is a diet Coke or an orange juice.
You will find that everyone has an opinion, though - nobody bats an eyelid if you have a G&T or a glass of wine, but if you decide that you want something other than squash you will be told not to 'pretend', or be asked why you aren't drinking, or why you want something a bit different from sweet children's drinks. It's strange, but it happens every time.
I don't like Nosecco, but there are other brands of non-alcoholic fizz that are acceptable, and some N/A wine is quite good nowadays. Otherwise, I go for soda water with ice and a slice, or a shot of Seedlip if they sell it.