For the first one, nice dress pants, a festive color top, if you want to do jeans, then nice dark wash jeans with a blazer and scarf, get your hair and make up done.
For the second one, I would dress up more, if it's nice restaurant, your guest will be dressed up nice and you don't want to be the only one dressed down.
If you have a nice shift dress with tights and flat boots would be cute, too.