I personally do not eat pre-made meals for that reason, unless I can scan some kind of bar code with the MFP app.

Other than that, I'd plug what you buy into the search bar and see what you find. If you don't know how much meat is there, I would grab a scale and use an equivalent at home so that you can eyeball the equivalent that is in what you have picked up. When all else fails, overshoot a little (but I don't recommend this as a habit).

When I buy wraps at school, I'll plug the ingredients that are in my meal individually and make my decision from there. Thus, a wrap with meat and hummus would look like this:

1 large green tortilla
Chicken breast (be mindful of not "cheating" yourself here)
Hummus (pick the measurement that best fits -- in my case it's 4-5tbsp)
1 cup spinach
1/2 cup banana pepper
1 cup lettuce
1 cup tomato

Add in your condiments and presto! You have your calories.
Truth is, though, that you won't know for sure what you're putting into your body unless you see it made right in front of you, or you make it yourself.

I have that problem too when I wake up late and don't have enough time to make lunch before I have to run and catch transit. For example, on Thursday I bought a Korean BBQ Chicken burger, and the restaurant's nutritional info was no where online. What I ended up doing was estimating on everything using other restaurants as sources. For example I searched "Korean BBQ chicken" and chose the highest calorie one among the list. And then I counted the calories for each item that made up the burger.

It wasn't exact of course, and I may have overestimated.....but in the end it is better to under-eat calories than overeat them. Also, for 'known' restaurants you can usually just go to their website and check the nutritional info out.

Also, if you need to go to restaurants or are hungry for snacks always try picking healthier alternatives. For example, instead of chocolate buy a granola bar with chocolate chips. Instead of ice cream buy a yogurt. Etc.

But, if you allow yourself room in your diet and are only counting calories in general (without counting fat/sugars) then you should be able to eat anything you want. (I just ate a chocolate bar and two slices of homemade pizza and am still under my calorie limit which is at 1300)

I weigh literally everything I put into my mouth on my food scale, but I couldn't do that in the college dining hall! Stick to the salad bar, lean protein, skip the bread/wraps/rice and any other carby add-ons unless you know the stats (a whole wheat tortilla can be 200-300 cals!). Hopefully the salad dressings at least have nutrition facts on them. Start meals with a brothy vegetable soup or a big salad, and if you really want something else too, have a small portion of a healthy entree. My college served small portions (because people usually took multiple dishes) so that was helpful. My easiest healthy meal every day was breakfast- my school had made-to-order egg white omelets with veggies, cooked in just a quick spray of cooking spray. Yay! They also had egg white & cheese sandwiches, and they had the packages of english muffins sitting at the station so I was able to check the calories.
I just did my best to guess and I probably overestimated calories a lot (better than underestimating, but still not necessarily a good thing- I was hungry and crabby a lot!)
My best advice...move somewhere with a kitchen as soon as you can, if your school offers it, and start cooking and weighing food for yourself! I moved into a lovely off-campus apartment with my friends my junior year, I saved thousands of dollars compared to the insanely high cost of dorm housing + a meal plan, and I was way healthier. win win win!