I had a good few events like this in early sobriety too Ali. At a friends wedding I decided to just run around taking photographs. It gave me something to do with my hands and stopped people from questioning where my drink was. I think I did end up taking more pics than the official photographer though!
I was also proactive on the drinks front. If you sort your drinks out first then no one can offer to buy you one and then pester you to drink alcohol when you ask for a soda.
Having a plan of escape is a very good idea too. I remember getting through the dinner fine but when people started to get tipsy I started getting nostalgic and wanted to join in. Stick close to anyone who you might be able to cadge a lift off, or drive yourself. Also a perfect ready made excuse for sobriety
Do not worry about what people will think if you leave early, they will just remember you were there, not that you left at 10 and were sober. Remember that no one really cares if you are drinking or not. It has taken a long time for me to accept that, but people rarely notice and even if they do it's your company they want, not a drunken entertainer
