Late night snacking used to be my biggest problem, but soon after I started eating bigger breakfasts, I noticed that I wasn't snacking at night anymore.
If you have an extra 1 cup measuring cup, keep it right inside your box of cereal. You'll remember portion control every time you open the box! This works for many other foods, as well.
To keep mindless snacking in check, find a good fidget. For example, I knit, so I keep small knitting projects by my computer, the TV, by my desk at work, etc. That way, I have something to do during downtime and I'm less likely to go find food.
Setbacks and mistakes are a very important part of living and growing. It's one of the most effective ways we learn. Don't dwell on them. Briefly study what went wrong, and move on, tweaking things a little to find your next good groove.
Put a clip or latch on your keychain and keep it clipped to your purse handle, totebag, etc. This way, your keys will always be easy to access and you won't be spending time digging through everything else.
When I'm not sure if my hunger is real hunger or 'mouth hunger', I pop a strong mint (like Altoids™), in my mouth. If it isn't real hunger, I don't really want to put anything else in my mouth after a strong taste like that.