What I do is just get as close as I can. For the lasagna, I'd probably look on The Daily Plate at a bunch of different lasagnas and then pick one to use the calorie count of. I would give an honest estimate of how much dressing I thought I ingested. Like you say, you can come pretty close on the bread and the cake.
It's not perfection, but it will at least give you a number if (like me) you feel it's important to log your food every day. It looks like you've already been extremely successful at losing so you're obviously being really careful and attentive whenever you can. I am early enough in the game that I can afford to be a little "estimate-y" from time to time, so I try not to worry too much about situations such as you describe. It's important to be accurate most of the time, but it's also important to enjoy life and sometimes that means a piece of really cheesy lasagna.