Let's define the term "cup". You can make a lot more in the USGI canteen cup than you can in a GSI or Olicamp Nalgene cup. There are small pots/large cups that fit over the bottom of Nalgenes which are about the same volume as the canteen cup. The NATO waterbottle cup/pot is about the same size as the Nalgene cups, and those are bigger than what you are using by quite a bit.

For the little ones, not much you can do. I've made ramen, rice, mashed potatoes, etc in my Olicamps, and so long as you add water and completely debone, you can stew a small rodent in one. But you are constantly adding water, not very efficent. They also make you enough water to rehydrate a freezer bag or LRRP-type dehydrated meal in the meal's bag. I don't know if that qualifies or not for your purposes.

Tip- if you have a side cutting can opener, cut the bottom of a coffee can off (or the top, if your brand doesn't have a pull off lid), but KEEP THE LIP. This will make a perfect lid for the GSI or Olicamp cup, which means your water will heat faster, and you can even heat something on it while the water boils. If you are very careful, and add a drag wire to your handles, you can theoretically turn an Olicamp into a micro dutch oven this way, but I've never tried.

In the USGI cup, I've made small soups, baked small bread, all kinds of stuff, but the key word is SMALL. It's a bit over a pint, I don't remember the exact amount. You can make quite a bit in that, but you have to be used to working with it and you'll only cook for one.

My three favorites are:

NATO/British pattern mess kits- ditch the third, inner tin, you don't need it. The two halves give you two things to cook in, each can hold about a pint of stuff with room to cook, and they nest, so you get a pretty much squash proof container for your delicate items. I use one as the shell of my not-so-a-pocket survival kit for that reason. I've fried, baked (the two halves turn into a quicky oven very nicely) and boiled in the ones I have.

Coffee can: Cheap, common, and it's a good size. You can also wedge an Olicamp or GSI cup in the mouth of it if your coffee brand has the pull off inner lid, or slip it onto the bottom and wedge it on as a two-compartment cooking kit. Holds almost a liter of water, and while it might vary a little by brand and size of can, you can use the ribs as a rough measuring guide. Down side is no handle, but pliers are a good thing. I usually cut the bottom out of another can, as above, and keep that as a lid under the plastic one (the space between them is a good place to stash snare/bail wire). I've boiled a lot of stuff in them, and my only caution is to test your pot before you put it in your pack- not all of thier glues are heat stable, and the last thing you want is a liter of soup water going into your fire as the bottom falls out of your pot.

Walmart grease pot: About a liter and half, feather light, and pretty cheap. Down side is that it dings up pretty easily, has no handle (pliers again) and the rim needs to be ground off or you need to carry something to clean under it. I like the lid, but replace the handle on that with a flatter one, and I always suggest keeping the strainer tray as it is a good spot to put little stuff from your cook kit, can be used as a steamer, and if lined with aluminum foil, it's a good backwoods fry pan. Big enough to pack a lot of stuff into, and I've even seen people use it without the lid as a buttcap for the end of thier stuff sacks. Big problem is finding them- they are in a funny spot in Walmart, look around the toothpicks and the salt shakers, and they may be going away becuase they are designed for those of us who belive in the right to keep and eat transfats. I'm not sure I trust it enough to use it as a dutch oven though, due to it's love of getting squished out of shape.