Depends on your time, budget, current resources, and skill/efficiency in sound design.
If you have access to Adobe Audition, then you should be able to download a decent library of canned effects from the adobe content download (it used to have the whole library built in and you could preview everything and then only download what you needed all inside the software; it was beautiful and yet they discontinued that [/rant]). Your teacher/university/classmates might have access to sound libraries. If you have a studio suitable for foley, you can record your own. Also the more you know about design and layering multiple effects to sound like one effect can greatly improve quality. In a pinch freesound.org is a decent resource, though I'm a little hesitant to recommend it. While everything is supposed to be creative commons licencing, there isn't anything stopping someone from uploading someone else's copyrighted work and you'd still be responsible if you used it.
Music is a whole mess. If you have a budget it gets much easier. GMP Music has tons of bed and background music at fairly reasonable rates. Other things such as Audio Juicer have options for quickly creating tracks at particular lengths as well as instrumentation used. However, both of those will require paying per track or per album/volume (there are several other professional sources, Pond5, AudioJungle, someone else feel free to chime in). For free music, the best I could say is ask local bands if you can use their recordings (original works, not covers). Maybe someone else has a better lead for free music, but I've found that trying to find free music takes more time than the cost of the licences from something like GMP.
Actually, if it doesn't already exist, having a list of places with readily available assets for production, would be rather nice.
I went to a big school, huge music department and for one project we did, we just asked some of the students in the music department to compose for us---all it cost us was some pizza and credits in the video.
Johnny Cuevas, Editor
"I have not failed 700 times. I have succeeded in proving that those 700 ways will not work. When I have eliminated the ways that will not work, I will find the way that will work."
---THOMAS EDISON on inventing the light bulb.