I toss pieces of pepper to my orange heads frequently. Just make sure no stem pieces are on any of the pepper - the same for tomato. While the fruit is perfectly safe, the stems and leaves of tomatoes, peppers, and potatoes (all in the family Solanaceae) are toxic.
As for the smoothie.. the Inta site looks suspicious, there is no nutritional information (unless I'm missing it) and vague over encompassing health claims. It could be possible that extra calcium is added to the smoothies, though, which isn't good for roaches. If the cereal is still good, eat it or share it with someone who wants it. Sell by dates are more or less a suggestion on items like that.