L.B.
My husband coaches soccer and tball. I think the coaches will appreciate anything you give them. My personal opinion? The gift card is best. To a restaurant, sporting goods store, coffee place. Gifts are more difficult since they require personal knowledge to get it right, jmho.
To ABM: No, gifts for coaches are not neccessary, but I can tell you have absolutely no idea how much work it is coaching kids, getting the practices scheduled, being there EVERY practice and game whether or not your kid is there, wrangling little kids to keep them focused. I always appreciated my kids coaches but now that my husband is one, I really really appreciate the effort that's put in by these volunteers!