While they can
survive without feed formulated for them, it would not be good for them for any length of time. If you are just having to wait until the weekend to make it out to get proper feed, you can feed them boiled eggs crumbled up (or scrambled eggs), unsweetened yogurt (not a lot, just about a tsp mixed in with the eggs), oatmeal, wheat bran, quinoa and diced fresh greens/vegetables.
I would not recommend doing this for an extended period of time as there are nutrients that they absolutely need that is not present in feeding just purely "kitchen scraps"....as well, if you are feeding them left overs, be very careful. Most people eat meals very heavy in sodium (especially prepackaged meals/vegetables) and fats.
As Flockwatcher said, there's a great treat list. And, if you do a search for "own feed" or "homemade feed" or such as that, you'll find quite a few threads on the subject.
Welcome to chickens!!
And, hey there, Flockwatcher.