I work in the school system and I will tell you the things we have enjoyed at my/our school. To give you a detail of the school I work in, it is "the" school in our county. It is a high school that has 1600 students. I say this because some of the things I am going to post might offend. But they are honest. It is an old prestige school that the rich kids go to. Recently during lunch a few of us discussed this same issue.
Lunch is a wondeful treat, however, we are leary of home cooked foods. Normally throw them away. Just not too sure how clean people are.
Fresh fruit is nice. Apples, pears, etc
Breakfast is also a big hit. We love biscuits, muffins and bagels. Once again not homemade.
Coffee is also a treat. While we have coffee, sometimes it is nice to have special coffee as a treat.
Gift cards from Target is always a treat. Target is a major
Flowers is a nice gesture but to be honest if it is given to the office, no one in my school sees them, except office staff. Giving them to an individual teacher is nicer.
Remember that most schools are strapped for money and supplies. While we have an excellent PTSO group at the school I am at classes room teachers still suffer with supplies. Normally they have to buy them with their own money. Mostly classes that are hurt are the Special Ed type classes. While you would assume Art is hit really hard, normally people remember them and either buy supplies or send some in or even donate money. But those that teacher occupational students or special ed often buys supplies with their own money. For the record I do not teach any of these subjects, but a good friend does and she has opened my eyes.
Remember there are all kinds of giving. You can always donate your time so the teacher could have a few minutes to have the lunch your brought her. This is a huge hit in the elementary schools.
I am just typing ideas. If I offend anyone I do not mean to. I am only giving you the ideas that was recently discussed in our 1st floor work room.
Once again this subject is broad. Some people might post about giving gifts to the whole staff while others are posting about giving to their child's teacher.