This app was mentioned in 3 comments, with an average of 1.33 upvotes
It's not a smartwatch app, but it has a smartwatch component.
I use BRING! for my grocery list.
As for games, I'm a sucker for tower defense games, and was rather fond and impressed by the (somewhat short) Guns'n'Glory (There's no guns, just wizards :P )
https://play.google.com/store/apps/details?id=com.hg.gunsngloryheroes_wear
I really liked the super simple and buggish Guns 'n Glory Wear.
It hasn't been updated in almost a year, and it's pretty short with little replay value, but it was fun for about a week or so.
I haven't looked into games since I first got the watch, but I went through most of Spooky House Games and am pretty convinced I'd rather play on my phone (or NIntendo 3DS) than on the watch.
I'm rather fond of Guns' n Glory
https://play.google.com/store/apps/details?id=com.hg.gunsngloryheroes_wear
It's a bit short, but it only costs 1 USD, and I enjoyed beating the game several times.