My job involves a lot of mandatory fun style meetups in bars. If I'm not excited about spending money, I order a club soda, and mingle. Sometimes the bartender charges me, but they frequently wave it.
If it's a sit down dinner, instead of a bar mingle, I follow the same club soda route. If anyone asks, I say I ate already, and I don't want to drink. No one has ever pushed me to drink, or forced me to get a meal. I've realized that t's one of those moments when we feel conspicuous, without actually standing out enough for people to notice.