Another note on oatmeal--I like to add a spoonful of powdered milk for a fuller flavor. When I'm traveling, I'll make up little baggies for each breakfast, with the oats, powdered milk, raisins, and a bit of brown sugar. Just transfer to a bowl and add boiling water.

ETA: Another thought--if you are eating fast food, some of the weight gain might actually be water retention from eating saltier food than normal, especially if you're fluctuating so quickly over the week.