Right, you asked for it, so I'll give you a basic jist on how I think first dates with some Sanses (or general UTMV characters) would go! Feel free to suggest/ask for others.
Starting off:
Sans (Classic)
Is it really a date? At the start, you had to double check your messages after a while at his house to confirm-- yes, you did set up a date.
It's nothing special, at least from first glance. I see Sans having dates or trying romance as a big step for him. It's a lot more mental effort for him than it is for others.
The first date would be spent at his and Papyrus' home. Whilst he thought he should take you out somewhere nice, he knew neither of you would really be into that... Okay, maybe you would like it. However, he would definitely leave mid-meal if you went to a fancy restaurant. Home it is.
Despite how relaxed it all is, he's noticeably closer to you. By the end of your date, he's likely leaning on you for a nap.
It'd be... relatively quiet? He wouldn't be forcing a pun out of himself, is what I mean. He'd drop natural jokes-- or rather, flirts-- mainly regarding how nice you look.
Papyrus would cook a meal for the both of you! He wouldn't do anything else, though.
You'd probably watch a movie, and you'd get to pick. You'd watch it, but you'd swear that he wouldn't.
You'd feel his tired, calm gaze on you whenever you weren't focused on him. Otherwise, he'd be absentmindedly staring at the screen.
His hand would be around your waist and have you pulled close to him by this point.
It's not a lot for a date, but that's okay. It doesn't have to be. He got to lounge with you, and you didn't seem to mind all that much. In his view, that's a successful date.
He'll definitely ask for another.