Well, if you believe the figures that Google pops up with when you type in “calorie info [food]”, you’re looking at the following:
[ul][li]chili con carne: 256 calories per cupwhite rice: 206 calories per cupsweet corn kernels: 132 calories per cup[/ul]So a two-cup container of chili, straight, will give you 512 calories. You lose 50 calories for every cup of white rice you swap in for chili, or 124 calories for each cup of corn. So you could do one of the two options below and still stay under 500 calories:[/li][ol][li]1/4 cup rice, the rest chili1/10 of a cup of corn (about a tablespoon and a half), the rest chili[/ol]This makes a couple of over-simplifying assumptions: first, that the chili served at your local cafeteria is actually 256 calories per cup. This could vary a lot depending on how the chili is prepared (amount of fat added, type of meat, ratio of meat to beans, etc.) [/li]
Second, we’re also assuming the volume of the chili doesn’t permeate into the rice or corn when you add it. This is probably a reasonable assumption, since only the liquid part of the chili would be likely to do so; most of the calories would be in the solids, which would “drain” a bit but would probably still take up most of the same volume. If the chili is particularly soupy, then you might end up adding more chili, so your calorie count would end up higher than you expect.
Finally, note that the calorie savings are really in the corn, so the more of that you can stand, the better. Subsituting rice for chili probably doesn’t save you all that much in terms of calories (unless your cafeteria serves a particularly rich chili.)