Sans's expression is best defined as cautious--sure, things seem to be alright so far, and the snowmen are gone, but Sans hasn't decided things are actually completely safe yet. But it is Christmas/Gyftmas, and Sans is not missing out on giving Papyrus some gifts, which he's carrying around in a paper grocery bag. He has to make sure Papyrus doesn't see him sneak in, though, so he's got plenty of time to say hi to Daylight.

"Well, I haven't gotten a trip to the lake yet, but there's still a lot of time left today."