(Can I) get you something (to drink)?
Can I bring you a beverage? Hi ladies, welcome to our restaurant. Get you something to drink? A: "Can I get you something to drink?" B: "Nah, I'm fine." You must have worked up a sweat out there! Get you something? Cold lemonade, maybe?
(Could I) get you something (to drink)?
an expression offering a drink, usually an alcoholic drink. (Compare this with (Could I) buy you a drink? Also used with can or may in place of could.) Bill: Hi, Alice! Come on in! Can I get you something to drink? Alice: Just a little soda, if you don't mind. Waiter: Get you something to drink? John: No, thanks. I'll just order dinner now.
See also: get