Your content doesn't exactly match your title -- are you talking long FILES as in number of lines, or long LINES?
I don't tend to write single long lines as I practice the "rule of 76" -- where if a line were to break past 76 characters I use whitespace to break it into pieces. The "enter" and "tab" keys are your friend!
As to long files, that's where bothering to use verbose names comes into play. The search function in your editor is your friend! Use good and meaningful names, if single functions/code blocks are excessively long add comments to your closures so you know WHAT is being closed. Good naming conventions and good commenting can go a LONG ways towards simplifying working with large codebases -- whilst creating things like "function tWwtCent" (that's taken straight from a codebase I cleaned up for a client last week) deserves a good swift kick in the groin. Particularly when what the function does resulted in a meaningful name of "transferWindowToClient" -- reeks of "wah wah, I don't wanna type!" derpitude!
... and you can always break up code into logical sub-files if need be. There are cases where doing so makes sense (when you're pushing up past 50k of code) and cases where it makes no sense.
Also depends on what language you're working in. Often times with things like HTML/CSS or client-side JavaScript if you have enough code for this to be an issue, you're using too much damned code! See the mouth-breathing halfwits who vomit up half a megabyte of CSS to do 48k or less' job, or a megabyte or more of JavaScript on pages that don't even warrant the PRESENCE of scripting... gets even worse when you see 60k or more of HTML doing 16k or less' job. It's SCARY how often I see codebases that are literally wasting five times or more the code needed to do the job.
See the mind-numbingly idiotic halfwitted mentally enfeebled steaming piles of manure that are "front end frameworks" -- which by their very nature make you write as much if not more code, make things harder to maintain, piss on accessibility from orbit, and almost universally finish off by wiping their backside with the very reason HTML even exists in the first place. THEN people have the unmitigated gall to call these dipshit dumbass train wreck laundry lists of how NOT to build a website "easier" EVEN when they've ended up writing five times the code!
Because of course, doing more work than needed is "easier". Sure it is.
Bottom line, if you're REALLY having this be an issue, you're probably doing something wrong... like using more code than you need to, relying on poorly written code from others without knowing how to do it without outside help first, or just plain not having good naming and commenting practices.