For a bugout bag you'll need a good first-aid kit. Also, your needs will vary pretty dramatically depending on whether you live in an urban area vs. a rural one.
I'm assuming you carry a cellphone, but I would put a prepaid cell in your bugout bag as well along with a map/compass. Also stick some meal replacement bars in your pack, you can eat them before they expire and replace them as needed (assuming you live in a fairly populated area where you'll have easy access to food).
I think preparing for the first few days (maybe a week) is all that's really necessary, considering that if the disaster is massive enough that you're unable to access supplies/shelter within a week, a bugout bag isn't going to do you much good for longterm survival.
Check
this website out for a ton of good information.