The best gift that one can give a teacher is a photo frame with the class picture in it. She/he would remember and treasure it. If that is something common, a book, a lovely painting or even a lovely pair of silver candle set would do.
A gift card to a casual restaurant is a sensible gift. A gift card to a store that sells a wide variety of school supplies is practical. If you are well-acquainted with the teacher, you can confidently give something that you know the teacher already desires.