When using SQL Server Integration Services, I like to keep things flexible and therefore I keep any hard coded names in variables. This means using the expression builder quite a lot, but the problem is the font size for the actual Expression is way too small, especially when writing code.
I find myself copying and pasting between SSIS and Notepad++ a lot, There must be a way to adjust the font size but I haven't been able to find it.
Another option is to grab BIDSHelper. It's a free addin to visual studio. When editing variables, you have a new pop up window to handle expressions. It gives you a bit more real estate to work with. It unfortunately won't help with the derived column transformations. I find that if my expressions scroll off the pane, that's usually an indicator it's time to push the logic into a script transformation.