Why did you skip lunch? Skipping meals is a big no-no! Drops the blood sugar too much, triggers the 'starvation' response in the body, binge eating, etc. Next time, bring along a healthy meal or snacks to nosh on. I can't imagine the mood I'd be in if I hadn't eaten all day.
No one can sabotage a diet if you don't allow them to. If you were full up on crudites and home-made humous or white bean dip, fruit, home-baked low fat muffins (substitute applesauce for oil), a healthy sandwich, etc., those crisps and guac wouldn't have loooked so appealing. Try making your own crisps by baking chipatis brushed with olive oil in the oven.
Try a more well-rounded breakfast - porridge/oatmeal with an egg-white omlette, yogurt w/muesli, etc.