There are so many good thoughts in this thread on this subject. I retired after 31 years of teaching in 5 states. Salaries vary wildly and most are dictated by cost of living issues.
The best gifts aren't gifts, as several have mentioned. Although gift cards and supplies are terrific to receive; don't get me wrong. Those gifts help in so many ways, as does volunteering.
But my best gifts? Parents and students who stay in contact to let me know how "my" student is doing...even afer I moved all the way across the country! That's my best gift...to know that I did my part in educating a future productive citizen. Quite a few have graduated from universities and two are military pilots! (I taught 2nd grade, so keeping in touch all those school years is something exciting to me.)
To those of you who volunteer in the schools and donate supplies and gift cards, bless you. Your example of caring for others is being watched by the small children in your care. They will remember. Those lessons will transfer. And if there's a teacher who really went the extra mile, it's never too late to send a note telling how much the teacher helped. (Most schools will be kind enough to forward those letters if the teacher is out of area.)
Off the soapbox...