Oatmeal is another decent one. Sometimes when I'm really hungry but can't ingest a lot of calories, I make myself a bowl of oatmeal. The plain oats are, of course, better for you than the instant ones full of sugar. Although you can purchase lower-sugar versions of the instant oatmeal now. I still feel the plain oats, especially the whole rolled, is better for you, though.
But the best things to fill up on that are healthy and lowcal, for the most part (unless you grab bananas and avocados or something, but they're still healthy) are fruits and vegetables.