Pretty obvious one this: drinking plain water. It seems oddly easy to think you are hungry when really you are thirsty, and water doesn't seem to have the same triggers for having something to eat with it that other drinks do. I have a glass first thing and have a drink of water whilst preparing meals, and any time I start feeling peckish. I try to keep water with me when out and about to avoid cafés and shops as for me it never feels 'worth it' to have just a drink and I end up buying something to eat. The other side of this is that because I don't go to cafés often, when I do I feel I can have something to eat if I do fancy it, because it isn't a habit.