I know what you mean! I struggle with this sometimes too. Especially, when my days are longer than usual, out of routine, and on top I am stressed out. This regularly throws me overboard, but I got great tips from many other sparkers to help with it.
If the water doesn't work, maybe you can eat something better than the swiss roll? Like a string cheese, or some cut fruit or veggies? While you munch on that, you can walk away and start distracting yourself until the craving goes away.
I also noticed that little prepackaged treats (only chocolate!! I stay away from prepackaged salty stuff like chips and crackers) help me to stay with one portion instead of eating the whole bag. I need a little chocolate once in a while, so I pick stuff like ghirardelli mini squares with raspberry filling. They say 4 squares is a serving (200 cal), but I try to stay with 2 because then it's a 100 cal treat. :) They taste fantastic, and often satisfy my chocolate craving. Maybe that's something that could help you?
Don't worry about failing once in a while. We all do. I still struggle with it my self too :)
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