Estimating Servings

I would recommend spending some time while you're home learning what different quantities look like. Focus on volume/size (cups, etc) rather than grams, as that's typically easier to measure.

Measure out 1/4, 1/2, and 3/4 cups of shredded cheese onto a plate. Study how much space it takes up. Compare it to something you can always access or that you know really well (e.g., the size of a baseball, a fist, something like that). Do similar things with meat, bread, etc. I wouldn't worry too much about veg (other than starchy veg), as typically they have very few calories anyway--even if you don't log them at all, it's unlikely to derail you completely). There is also good information online and in many diet books about estimating portion sizes (e.g., one serving of meat is about the size of a deck of playing cards).

Spend time studying the sizes of known portions. Then, when you eat out, study your food for a few moments before digging in and estimate the quantities. You're probably better off entering estimated quantities (e.g., for a salad, entering the lettuce, dressing, cheese, etc separately) than trying to log the whole entree (e.g., caesar salad), since preparations and sizes vary so much. (The exception to that, of course, is if you happen to eat at a place that has nutrition info listed for its meals.)

This isn't as accurate as actually measuring everything, but it's better than just guessing (because most of us are way off until we actually start to measure).